What is a good first thing to buy with guild marks?

[Sojiro]

I went tanning then tawing first as well. After that its really up in the air on what you want to spend your marks on. I think I did cobbling next (at the time I was making lots of shoes). After cobbling I picked up Brand of Lightning, which at first I was disappointed it wasn't a passive skill, but got over it. Since lightning is one of the more brutal of instabilities, directly affecting your progress rate, BoL is really nice to kick on when lightning element destabilizes and really helps to get it back in control.

I'm actually looking into picking up Brand of Wind from WVR next because the "Brand of" abilities really help get elements back in line fairly quickly. At this point i'm just buying the rest of the cheaper ones, and then i'll grab the last two expensive ones I have left (clean slate and bold endeavor). So far I have heard very little good about clean slate, people have said it seems broken and I don't know much about bold endeavor.