If you pick a crafting class, pretty much any of them, you can burn through the first 20 levels easy as the materials are gotten easily from the NPC nearby or in the market area of the city. Make sure to do the quests for your crafting class as well as you go along for some free crystals and gear.

If you want gil, you can do all those crafting quests up to level 10, and sell the crystals on your marketboard (but that is unlocked through the MSQ if you haven't gotten that far yet). Depending on your server, even crafting gear you get from the class quests can get you some gil.

Hm ... overall, I found furniture sells good, as players are always looking for stuff for apartments and houses. Could also try making HQ weapons and armor. Food and drink doesn't usually sell unless it is a much higher grade for raiders. I like to look up what materials are used for and see if they are worth selling on the MB or to an NPC. Gotta play the market!