Contrary to popular belief, your first tattoo should be pretty big. Mine was on my back (pic in my profile) and its a good size. You get all the really great detail once its that big, otherwise it just looks like another tattoo that you got spur of the moment at an Inn out in La Jolla.
Spend a lot of time developing a concept, then even longer finding an artist you really love. Set up a consultation once you've settled on a concept and let the artist run with the idea: it's what they do. Also, think about your subject, and if thats something ur artist is good at. For example, some artists specialize in portraiture, others in flowers and other horticultural elements.
And finally, budget. My half sleeve is going to run me almost 3 grand, so be prepared to fork over cash for a great tattoo.