Easy guide to enhance shammy gems:
Relentless Earthstorm. Always. Always. Always.
8str, or 4str/4crit gems IF there's a damage-oriented socket bonus.
The gem from Heroic Steamvaults + one 4str/6sta gem to activate RED, only in damage-oriented socket bonuses (not stam ones, unless they're all you have), and never any more than those 2 blue gems. Blue gems = fail.
Another piece of advice: forget you can wear mail. Full leather. Leather badges bracers and boots, leather chests, leather helms, leather everything. Pretty much the only mail pieces that are worthwhile are the legs from Kazzak/Reaver/Hyjal, the badges gloves, the S3 helm, plus the nonset S3 pieces while you're still gearing up. Everything else should be leather. Why? Intellect and mp5 are both wasted stats, they might as well say +healing and spirit for all the good they do you. There's a few items that are close, but the leather items are still better.
EDIT:
Go here and scroll down to point 3. Use that, plus Yo!'s sim linked farther down the post, to assess what items you should use.
Edited, Feb 14th 2008 5:09pm by lsfreak