[Veni Vidi Vici]

I'm not sure about the qualifications or if you even need to go get some sort of certification in order to practice this, but what my friend did (and pretty much what any logical person wanting to become good at this would do) is ask around at different tattoo parlors for an opportunity in apprenticing an already established artist. What some people even do is offer to put in some work in exchange for lessons. If I were aspiring to become a tattoo artist, I would definitely do what some people above said and try to learn from the best. I assume there could be college classes (and some might be useful) but in my opinion, learning at the job, and apprenticing would be a better way to go.. Good luck! Carpe Diem.

PS. You should look into whether you need some kind of qualification/license in order to do this. You can ask an artist if/when you go talk to one!