Archvale

Crafting can be done at the anvil in almost every town, and requires resources you'll find in the world tiles of each region. Enemies will drop some resources, and others are found by breaking appropriate objects in each regions (such as piles of rock, in many regions). You should be smashing up all of the resources you find as you explore the overworld, and you'll likely get many without trying, because you'll end up breaking and collecting them while fighting enemies.

Crafting is a good source of higher level gear, as each time you head through a new region of the overworld, you'll be able to collect new resources from that region, and therefore be able to craft new gear with those new resources. So, every time you head to a new town, you should always check out what new gear you can make. Personally, I always focused on crafting the next best head and chest armor I could make, to keep my defense up. This is because each region contains a few chests that each have a new weapon in them. So, you'll get new weapons naturally from chests, but armor only comes from buying it or crafting it. Therefore, focus your crafting on armor.

If you're like me, you'll likely find that you don't craft anywhere near 30 items during the natural course of the game. However, you'll likely find you constantly have an abundance of resources, especially ones from regions you've long since passed, and whose gear is not a viable level anymore. What you can do then is craft the same low level gear over and over to use up your old resources. This both progresses this achievement and gets old resources out of your inventory, since you'll never used them anyway. Just discard all of the low level gear you craft to make room for more. By the time you're done with everything else, you should have a huge amount of resources to be able to grind out however many more things you need to craft for this achievement.