Short Term.

Purchase stacks of things.... Infinite Dust, Raid Flasks, Gems etc on weekends, for low per each price.
Relist on weekdays, as singles or smaller stacks, for a lot more per each.

Sunday is the cheapest day to buy things.
Fri/Sat is the most expensive days to list things.

I buy 25-35 stacks of dust on Sun, and sell them all by the next Sat. I pay 20g per stack and sell 2g each (100% mark up).



The next arena season is coming soon.
Stockpile gems and enchants, mats for enchants, etc.
Sell these with a substantial mark up, when the season goes live, and people have the new gear.
The same holds true for new raid content.



Long Term.

Have one of every production profession, on an active team PvE progression team.
The team which you run heroics with, possibly raid with some members of the team (or all of them), the team which grinds reputations up.
IE, the team which will have the maximum number of recipes.

You'd want 1x each crafting (not gathering) profession at maximum level, with as many recipes as possible.

Then look at average selling prices for top end gear.
And the average price for the mats to craft these.

Purchase mats when they're cheap.
Also advertise: /Trade Buying every stack of "x" you have for "y" gold per stack. Send CoD to "z" toon.
Pick a price which is advantageous to you, and is still decent for the gatherer.
They'll sell directly to you, not losing the AH cut or paying 0 to 5+ days of listing fees.

Do this with several toons, covering every production skill with combines that sell well.
Ideally, you'll be crafting 20+ high end items, between your team.
Buying mats cheap, is less profit (per piece) then farming mats yourself.
It is also much more profitable (per hour) by a very massive margin.

Don't flood the market with your stuff; 1 or 2 at a time, is ideal.
If others are listing the stuff, try to agree on a price with them, rather then getting into a price war where neither of you make jack.