search up your local artists first and pick someone who can do really good work similar to what you're getting (ie, if you want linework or a small black design, look for artists with nice clean lines, if you want good color, look for that, good shading, etc.). also, consider that there are certain parts of your body where a tattoo will "fade" and need touchups more quickly, or something... for one thing, your inner forearms and legs/feet have thinner skin and the ink will spread and become "blurry". that sort of thing. also, make sure the place you eventually choose is sanitary and follows health code. infected tattoos are not fun. also, very basic and obvious, but know what you want tattooed and why you want it!
Looking up basic after care would be a good idea, so you can get the creams and such you'll want. If the design is large, complex or needs blocks of colour, it'll probably take multiple sessions. You might want to consider locations as certain areas (especially thin skin over bone such as the outside of the ankle) can be much more painful, and others more prone to sagging with age.
Beyond that just remember it's going to be there for the rest of your life, so don't do anything silly.