This is a pretty good method you should use before all patches.
It works like this:
1. Go to patch note site (I Think it's (World of Warcraft Europe -> Info -> Test Realm)
2. Scroll down to professions and look what's new and what's changed.
EXAMPLE:
Notice that is a new recipe to scatter Void Crystal to two Large Prismatic Shard.Code:Added several new tradeskill items to the new Sunwell Daily faction vendor:
- Enchanting recipe to shatter a Void Crystal into two Large Prismatic Shards.
- Enchanting recipe to increase Defense Rating by 15 for chest armor.
- Three jewelcrafting recipes to cut gems with spell haste from Dawnstones, Talasite, and noble Topaz.
- Two new meta gem recipes.
Maybe this isn't the best example but it shows you the basics.
Here is another one:
GREAT! A new recipe. We want that.Code:
- Broiled Bloodfin now increases resistances to all schools of magic instead of increasing Stamina and Spirit.
- New recipes, Charred Bear Kabobs and Juicy Bear Burgers, can be purchased from either Bale (Horde) or Malygen (Alliance) in Felwood. These recipes requires 250 skill to learn, and are created from meat found on level 48-56 bears. This will aid players in leveling up their cooking skill to 300 without fishing.
For this recipe you need '48-56 bear-meat'. This will be greatly used by players who struggled on the last skills to 300.
Now simply go buy all the bear-meat off AH and resell it for the DOUBLE price.
Let's take a look at another example:
Here it may be a good choice to buy some materials for this enchant and resell it higher.Code:
- Reduced the materials required for Enchant Shield – Resistance
So simple do this:
1. Check the big-patch-notes, under professions
2. Check new recipes and changed ones
3. Buy the mats for the new recipe and resell it
4. Profit!
Hope this explained more how to do it and where to look.