XP should be commensurate with the values necessary for advancement:
-Defeating an enemy gets you 1xp
-Solving a mystery gets you 1xp
-Exceptional roleplay/player skill gets you 1xp
-Completing an adventure gets you 3xp

These are all up to the referee!
You could give 1xp to each player for completing a session
or

Allow the players to give out 1xp per superlative at the end of a session.