Gathering can bring in some great money, and save you money if you're hoping to grind crafts. Like Este suggested, each craft has gathering classes that work well for it. So Carp --> Botany; Culinary --> Botany (Harvesting, which is your off-hand gathering tool at special Harvesting nodes); Blacksmith/Armorer --> Mining; Goldsmith --> Quarrying (mining's off-hand gathering tool at special Quarrying nodes); etc.

So like Este suggested -- that dude is smart -- I'd suggest choosing which craft you want to level first, and then level the attendant gathering job.

There are a few exceptions that are noteworthy. For example, dyes -- which are used in pretty much every class -- you can get from secondary/off-hand gathering nodes from all classes. For example, red dye can be obtained from Quarrying nodes around Limsa Lominsa. Some dyes sell really well right now, since dyes effect stats. But that's going away in the next patch. So you can use it to make some money now, but it will be going away soon.