How to gear for Enhancement

The proper way to determine stat weights is to run the simulator with your stats plugged in.

http://elitistjerks.com/f31/t31667-enhancement_shaman_enhsim_dps_simulator/

If you're still leveling up or feel lazy, a general rule of thumb is as follows. These are ordered by priority.

1) 9% total melee hit (to cap special attacks, include improved dual wield here)
2) Expertise (until 6.25% reduction in parry/dodge)
3) 17% total hit (To cap spell hit. Note that improved dual wield does not provide spell hit.)
4) Crit and Agility (no real caps here)
5) More hit (until hard cap at 22%) > Haste > Int > Str > Attack Power > Spell Power

Note that hit has "soft" caps at 3% (for special melee attacks, including 6% melee hit from talents) and 17% (for spells) and a hard cap at 22% (covers everything, assuming 6% melee hit from talents).