Will be pretty hard to add shadows on black
This guide might help, as I guess you are painting them the 'classic' way.
http://uk.games-workshop.com/tau/getting-started/4/
For the cloth, you could mix chaos black and Scorched brown and paint it on (I think they did it in the guide) and then highlight it with regular scorched brown and keep the dark in the folds.
For the highlights on the armour, you could mix vomit brown with bleached brown and use on the extreme edges, or you could simply use burbonic brown for a similar result.
EDIT: Welcomme to the forums btw! I like your name, might you be swedish?
This guide might help, as I guess you are painting them the 'classic' way.
http://uk.games-workshop.com/tau/getting-started/4/
For the cloth, you could mix chaos black and Scorched brown and paint it on (I think they did it in the guide) and then highlight it with regular scorched brown and keep the dark in the folds.
For the highlights on the armour, you could mix vomit brown with bleached brown and use on the extreme edges, or you could simply use burbonic brown for a similar result.
EDIT: Welcomme to the forums btw! I like your name, might you be swedish?