I'm still working on this. I'm running a no-combat (so far), solo Modern campaign, so all my XP awards are ad-hoc. I'm a fairly inexperienced DM, and I'm never sure what to award for a session that's heavy on the roleplaying and skill checks but light on the actual CRable "encounters".
I don't necessarily want my PC to level up at the speed of light, but at the same time, I don't want him to suddenly be 6th level without really having done anything. So how do people adjudicate how much good RPing, critical skill checks, dealing with people on a diplomatic basis, etc, are "worth"?