Experience

Your character advances in power by gaining experience.
You gain experience by:
Killing a monster
Being part of a group that kills a monster.
Improving your skills through use (not quest skills).
Exploring the world.

You lose experience by:
Fleeing from combat
Recalling out of combat
Dying

The experience you get from a kill depends on several things: how many players
are in your group; your level versus the level of the monster; how many of
this monster have been killed lately; and some random variation. To gain
experience from exploring the world, walk around.

There is a list of places to kill for exp on the forums. Also try the
AREAS command for a raw list of mob levels.