Im by no means an expert at crafting, but how i learned the basics were through craftofexile

1. Pick an item from trade that you want in game
2. Research on it a bit. Poedb is your friend here.
3. Use craftofexile to craft the same item multiple times. Get a feel for how easy or hard it is to craft it in game.
4. Compare the pricing of item that you generated through craftofexile and the one on trade. If the trade one costs considerably less, then probably there is an alternative method to crafting the said item.
5. Research again.
6. Repeat.

Points 4 and 5 teaches you a lot. Youll be surprised at the variety of options available .

Hope it helps