Sneak
Stamina drain and stealthiness when sneaking.
At level 100
-60% initial sneak visibility
-20% light based visibility
-75% stamina usage
Earning experience
0.05/s while sneaking (+0.45 when undetected within the view range of a creature)
Crouch-walk near enemies that have not seen you for the big ticks. The troll cave shuffle (sneaking laps around a sleeping troll) is the classic power-leveling trick.