let me give you an example of how I normally do it.

give_trait Quintus RomanHero 5

What the above will do is give Quintus (the leader of the Roman Faction) the Roman Hero trait at the fifth level of it (the maximum I believe). I also noticed that you don't need quotation marks if the character only has one name.

Anyways, the trait names (and max level) can be found in only one surefire way... go to the data directory in your RTW directory and find the text file export_descr_character_traits.

This file has all the traits listed, the conditions, their effects, everything. You can even modify them if you want to create a 'super trait', but make sure you know what you're doing first... it's not hard to do, but you'd want to make sure that the enemy nations' characters' can't get their hands on it by accident.