If you want to reward players for certain behaviors (roleplaying, acting in character, avoiding metagaming, stuff like that) then you should maybe come up with a list of desired behaviors and give each one a challenge rating (or just a straight amount of XP).
On the other hand, maybe XP aren't the best reward (they're a good reward for the character, but maybe not for the player). Maybe something like a "hero point" system is in order -- when the players do one of the desired behaviors you could give them a hero point (or an action die or whatever mechanic you want to use), something they can apply to their actions. Some players might like that kind of reward better than XP.