Here goes (my preference):
After the gaming session, assign a few skill points for the things players
did. Forget about training, levels etc.

The player fought a tough enemy (ignoring the outcome of the fight):
increase combat skills (weapon skills/THAC0/whatever).

Players travelled through the mountains on mules? Increase riding skills,
climbing skill, or animal handling - if it was a difficult task, say in
winter, or over a two week period etc.

Player was hit several times in combat, lost consciousness/nearly died?
Increase constitution/hit points whatever.

Has carried a new spellbook around for a longer time period, studied hard
in a library (no need to roleplay this): increase spell casting skill/add
spell to repetoire (if you use a system with spell levels, only allow tough
spells later in your game).

See the direction?

I used to calc all the exps/carefully note every action on behalf of the
characters, add the same amount for good roleplaying - until I realized
        (I hope no player reads this)
I was just making it up in the end! I rounded everything, invented the rest
and distributed to my liking...

-- [ Everything's a fairy tale - and everything is true ]