Well, here's my tip I'll throw in the pot.

Patches.

PATCHES PATCHES PATCHES.

They are the BEST times to gouge people and make a lot of money.

Check the patch notes, when new recipes come out, make sure to clean out the ah of those items before servers go down and put them up for gouged prices. As people log on in the early mornings to get these new things crafted, they will buy your's out.
This goes for patches that release new items as well.

New arena season releases are also good for enchanters and jewelcrafters to peddle their wares on the release day when the masses get new pieces of items that need enchants and gems.

Tuesdays right after patches are also good times as well as arena points update.