Ok lets look at the two units:
Lictors - ok these are deepstrikers with rending, the tail and only a few wounds with not hte greatest save in the world. That means that they are fragil - one shot wonders. They are meant to appaer and attack the rear armour of tanks; sniper troops (e.g. eldar pathfinder - though tau firewarriors are another good target); and break up heavy weapons fire for a turn or two --(eg impiral guard guradsment with heavy weapons team). They are not going to earn thier points back by killing, what they are going to do is take down those snipers before they get your carnifexes - they are going to hold a squade in close combat for a turn to two - letting the rest of the swarm advance without comming under fire. Use them in groups of 2 or more - a loan lictor is not a great threat - also, though they operate independently, they work best in a group attacking the same target, though you can split them up if you wish - disrupt a whole fireing line.
Ravener: Ok four things about using raveners;
1) don't deepstrike them; they don't have the special rules of the lictor, so they can be lost on deployment and they cannot to any assaulting on the turn they appear - - easy target for guns. Instead make use of the fact that they are as fast as a hormagaunt and charget them across the battle field with the rest of the army
2) don't give them guns - ok you can, but thier bs is low nd giveing them guns mankes them overpriced for what you are getting out of them. Though if you do decided to go gunning, devoureres are best because of the re-rolls - though the short range means you will only get one round of shooting out of them. Deathspitters have a longer range, but only a single shot - with a bs that low its not worth the gamble.
3) don't group them up in 1 fast attack slot (unless you are using the others) split them up between the slots. This means that the when your opponeent fires they can only kill those in the squade that they target - even if they get 4 wounds, they can only take one ravener away. Run them near each other on the board to support each other in combat - attack the same targets.
4) always always always give them scything talons and rending claws - the kills from rending are always worth more then the extra attack from another set of scything talons. Note that the ravener blister does not come with the claws - but the 3 clawed rending claws from the genestealer do fit the ravener model very well - middle arm slot looks best.
Well that is about it - raveners a supporting assault troops, whilst lictors are deepstiking surgens.
