You join the guild, and then you look up recipies on sites like this, or Somepage.com. And then you craft stuff.
Yes, it's just that easy.
edit: To elaborate.
Here is a list of synth recipies for Clothcraft. And
here is a list of desynth recipies. I suppose Chocobo Fletching would be a good way to get to level 2 if nothing else. Or you could make grass thread by desynthing Yagudo Necklaces, and then turn those into cloth. I seem to recall that's what I did once upon a time when I thought about taking up Weaving.