Basics of a good list.

I wouldn't call them a must, I'd just say that they're the easiest to use for beginners who want to win.

Some units, paricularly bikers, are more difficult to use but can kill a lot more. For example, just by looking at # of attacks, Assault marines are immensly superior to 1-attack bikes, but can't turbo-boost, have a mere toughness of 4, can't get melta-weapons, and can't get plasma weapons. Also, if bikes are forced to be out in the open, they can at least turbo-boost to get an invulnerable save, whereas assault marines are vulnerable to AP 3 or 2 weapons no matter what they do or where they are (aside from getting into combat).

There are also units like scout bikers which are horribly underrated. They suffer from a horrble armour save and lack of weapons options, but are one of the only SM units which can get a first turn charge (the other unit is shrike's wing which can infiltrate, scout move 12", move 12", and then assault 6"). Therefore, if equipped with meltaguns, they can blow up vehicles with striking effeciency or get an important enemy HQ tied up in assault. Units like these don't cause much damage, but they can amplify the damage or protect other units so that they have an easier time.

I guess that what makes a great army list is to have units that support each other. For example, you could use the scout bikers to make a huge LOS-blocking assault while other slower units, like assault marines, move up behind them in the cover they've created to maximize their damage without any casualties.

Balance is also key in lists. Too much HQ will take up so much points that they won't be able to make up for the cost, but too much troops means that other more devastating units, like HQ and heavy support, won't get fielded as much as neccessary. For example, an army with 6 tactical squads with a lascannon each won't do as much damage as an army with 4 tactical squads with lascannons and a devastator squad with missile launchers. The tactical squads can depoy in fromt of the devastators to force Ld tests on the enemies that want to shoot past them into the devastators.

I agree with Ezekiel1990, balance and support is the main key to sucessful army building. No unit in your army should be stand-alone, they should be helping, or recieving help from another unit, either directly or indirectly. There are several different ways to do this:

---A very common example of direct support is the Chaplain-led assault squad. He lends them his Fearless ability and gives them his Litanies of Hate combat to hit re-rolls when charging. They lend the Chaplain a meat-sheild to be able to get to the enemy and number of attacks while in combat. Likewise, the Commander directly supports every Space Marine unit by lending them his leadership.

*shameless plug*The techmarine is also an excellent, but often overlooked, support unit. He can lend his Signum's shooting to hit re-roll to a Devistator squad, along with his Auspex for added security from infiltrators, or his power weapon and extra servo-arm powerfist attack to tactical squads. Have him follow your Dreadnaught or LRC in base to base contact to fend off nasty deep-striking meltas and repair when nessicary.*/shameless plug*

---There are almost countless ways to indirectly support units. One common one is to use tactical squads as fire-screens for more important/squishier units, forcing opponents to make Ld tests to shoot past them. Scouts, or scout bikes can also be equiped with teleport homers, giving thier much slower, but more powerful, Terminator brethren a leg-up when covering distance safely. Also there are distractions: putting an intimidating Land Raider or LRCrusader on the board will draw enemy heavy-fire from less-protected units, such as Devistators, Terminators, or other foot-slogging units. It might even draw thier attention away from that melta-toting Land Speeder zooming up the other side of the board...

Again, there are countless ways for units to support each other, so be sure to keep that in mind when making up a list.

Copied from the Deployment and Maneuverability thread

PROPERLY SUPPORTING YOUR UNITS

One of the major problems I see in newbie army lists is that the units in the list do not support each other well.

For instance, I commonly see pretty static lists with low firing range coupled with a single squad of infiltrators. In most situations those infiltrators arent going to survive very long because your threat range isnt far enough to keep them protected. The following is a list of armies and how they support each other well and why.

Below I have detailed some army variants along with what units to use in them so they are properlly supported.

The Static Army

These armies are generally characterized by low maneuverability and long range fire. Deepstrikers, infiltrators, fast moving units and vehicles have very little place in such an army. The idea here is to form a firebase that will annihilate anything that gets into range before it can make it to the lines.

Deepstrikers lower the ammount of firepower you start with on turn 1 and it can be tempting to deepstrike them into an area where they will be easilly outnumbered. Worse still, it may take many turns for your deepstrikers to arrive and you will need that firepower on the table to keep your squads out of close combat.

Infiltrators tend to be placed far forward, out of help range of the rest of your army. You CAN use infiltrators in this type of list but keep them close to your lines. Use the infiltrate to set up in cover or to compensate for lower ranged wepaons such as plasma cannons and heavy bolters.

People have a tendancy to use fast moving units to intercept or chase down opponents. In a static army they have a very different use. There maneuverability is used to confer firepower laterally. What this means is that fast units should still stay in line with the rest of your army, but move from side to side to lend firepower to where it is needed most. Never send these units ahead of the main force to harass your oponent. You want to leave them as little targets as possibel for as long as possible.

A quick note here. While static armies concentrate on firepower it is always a good uidea to have a countercharge unit or 2. By countercharge I do not meen you let the oponent assault you and then charge your unit into the fray next turn. Countercharge units are units with large assault ranges that can be used to intercept an oponents squad BEFORE they make it to your line. Assault squads are very good at this as their increased movemnt can let them get to where they are needed. Dreadnoughts also make good countercharge units although being vehicles they make high priority target.

A properlly supported static army would be comprised mostly of troop squads (tactical, devastator, command) with heavy weapons backed by laterally moving heavy weapon totters (termies, dreads, speeders, bikes, attack bikes) and bolstered by a unit or 2 of couterchargers (dreads, assualt squads, bikes).

The Forward Deployed Army

Forward deployed armies make use of forward deployment (Infiltrating, scout moves), deepstriking and fast moving units to fight the battle in your oponents side of the field. The ratio wich you use these units is imperative. Being a forward deployed army, it focuses on setting up most of your troops closer to the enemy and supports this with deepstriking and fast moving vehicles.

When using infiltrators it is important to have at least a few squads infiltrating together. It will take at least 1 turn for your fast and deepstriking units to arrive and so these squads need to be able to hold their own untill such a time. Full squads of marines and scouts are recommended.

This type of army need not be solely focused on close combat. There are many devastating weapons that are held up by their shorter range. Assault cannons, plasma cannons and heavy bolters are perfect examples of these. Between use of devastators and command squads you can infiltrate quite a few heavy weapons right into range of the enemy. A solid firebase for a forward deployed force can often do more for you then close combat troops as you can make use of any cover you infiltrate into to soak incoming fire where as in close combat, your oponents will have clear strikes at you.

As far as close combat is concerned, a mistake new players often make is to believe that infiltrators can make a first turn assault. This is not the case. The closest that infiltrators can be placed to the enemy is "at least 12" away". What this means is that regardless of what it looks like, a 6" moving squad that assaults 6" will always be at the very least 0.0000001" from the enemy aftfer an assualt move. This may not look like much of a difference to you, but the game cares. Infiltrators can not make first turn assaults unless your oponent has moved closer to you.

The one unit in the SM arsenal that can make a first turn assault is the scout bike squadron. When playing on a standard field with standard deployment distance (15" deployment zones seperated by 24" in between) you place the scout bikes at the front of your deployment zone (leaving 24" between you and your oponents deployment zone), make the 12" scout move before first turn (12" between your scout bikes and the oponents deployment zone) and on your first turn move 12" (now right outside the enemies deployment zone) and can make a 6" assault into your oponents deployment zone.

Close combat forward deployed armies are very good as well. The same rules apply as shooty forward deployed, but you simply tool the squads for close combat. Full scout squads are excellent for this as they are cheap, get Bpistols and CCW's and obviously infiltrate. Full squads are recommended as these are generally used to hold your forward position untill your assault squads, bikes and deepstrikers can make it there.

This army makes good use of the new castellan mines as your effectively shortening the size of the battlefield and can predict where most of the fighting will take place. As the catsellan mines do not affect your own troops you can litter an area with mines and not worry in the slightest about them.

The Fast Army

My personal favorite type of army. These lists only make use of units that can move more then 6" a turn. Speeders, bikes, assault troop and attack bikes normally make the core of these lists. Transports are not recommended as between their generally crappy defensive measures, problems with embarking/disembarking and not to mention being unable to fire its weapons when moving 12" they end up being slower then you would think.

Aside from modifying your FOC with traights or a different chapter, troops should be kept at a minimum as they tend to be slow. Decent options are 5 man lawscannon teams as they have the range to support you across the field, infiltrators and drop podded tactical squads. Usually these are kept at an absolte minimum as they do not move as quickly as the rest of the army.

Fast armies tend to be low on model count and more fragile then lists that focus on infantry. Because of this it is imperitive that you use the armies speed to outmaneuver your opponent. This army makes the best use of Baiting, reversed flank, denial of LOS and other movement tactics. Personally I find these armies work best when more focued on shooting. Assault armies tend to get bogged down in close combats witch reduces your maneuverability to pretty much nothing.

The Close Combat Rush Army

Pretty self explanitory. These armies use whatever means necessary to cross the battlefield and get into close combat as quickly as possible. This used to be done with rhinos, unfortunately as you can no longer assault out of a rhino coupled with the rhinos abismal armor value this has generally been abandoned. These days, your best bet for this type of army is assault squads and bike squads coupled with infiltrators and 1 or 2 deepstrikers.

It is important for these types of armies to limit the ammount of deesptrikers they use. With to few targets heading there way, your oponent can make short work of what you have on the table. It is recommended to take one or 2 deepstriking squads as they give you tactical options you would otherwise be lacking. Drop podding dreads and tactical squads are generally your best bet here.

Infiltrators are used slightly differently in this army then in a forward deployed army. Most of your strength in this army comes from assault and bike squads heading up the field. Your infiltrators are simply there in most cases to slow your oponent down and keep their infiltrators farther up the battlefield. The one exception to this rule is the infiltrating close combat army. This closely resembles a forward deployed army in that you are trying to infiltrate as much of your army, decked out for close combat, as possible. Optimaly, this is done with the traights see but be not seen and take the fight to them. This type of list generally deals with armor with a combinatoin of melta guns and powerfists. The meltagun has a secondary purpose of killing high armor troops the round you assault. This is especially handy when assualting terminators, necrons or modles that only your powerfist can damage.

The Drop Pod Army

As far as im concerned this is the most deadly type of army that the new codex gave to us. Every time I have seen it used, it decimates its oponent. Best for lists between 2 and 3 thousand points, this type of list is characterized by drop podding tactical aqnd command squads as well as dreadnoughts and terminators. The key your are exploiting here is 2 fold. 1) The drop pod itself is basically a piece of instant terrain. With enough coming in on the same turn it is easy to all of a sudden split the battlefield in the way that you choose. 2) The safe deepstrike coupled with the 2" deployment zone and being able to get out on any side of the pod you choose. This allows you t o make the absolute most of meltaguns and assualt cannons and boltguns the round you deepstrike. So long as you have enough podding squads, it takes one or 2 games to get used to how this army works. Once you have it though, it is probably the most frustrating type of army to play against.

Generally you want to use more squads then dreads or termies simply because their survivability VS cost ratio is better. It will be rare that you get most of your army at the same time with this and as such you do not want to be podding easilly destroyed things like dreads and small termie squads.

IMHO the best squad to be using for this type of army is a 10 man tactical squad with powerfisted sergeant and a melta gun. You may modify this with traights as you see fit, but for effectiveness sake, cleanse and purify coupled with take the fight to them are your best bets. This army makes use of short range firepower and assaults to deal with oponents.

It is imperitive that you start the game with nothing on the battlefield for this type of army to be succesful. Your oponent will have an easy time dealing with any units you deploy so keep everything to a drop pod as the name implies.

The Hybrid Armies

Hybrid armies make use of a little bit of everything and are what marines do best. As far as ease of play goes as well as ease of winning this type of list is the way to go. Generally ment to take on all commers, these lists have a little long range fire (generally a 4x missile dev squad and a long range dread) some assault units (generally your chaplain led assualt squad), some mobile fire support (LST's), some static fire suport (6 man tac squad with lascannon and plasma gun) some infiltrators (most commonly sniper scouts), some deepstrikers (close combat dreads in pods or terminators with assault cannons) and a vehicle or 2 simply for variety.

These armies are easiest to play because it gives you far more options then any of the other lists. You will not be particlularly strong in any one area, but with proper conjunction, these lists perform very well. The ability to use all the most cost effective units is obviously a boon. The mix of units also lets you adapt to your oponent while they have a difficult time adapting to you. This type of list is actually what SM are about.

Ok there are more of these, but I cant look at lines of text anymore so ill let this end here. Perhaps other people can put up other types of armies and explain how they support themselves and why they are good.