look on the net, find tattooists with good galleries in your area (some look they have been finger painted by a chimp!) Talk to mates with tattoos etc... the most important things to remember are:
A. Find a tattooist that's good at what you want, some are ace a colour and free hand work, but iffy at intricate black work and vice versa
B. A good tattooist will do a free consultation where they will look at what you want, see how it works with your body and give you advice on if how it needs modifying to work. ( a good picture doesn't always translate into a good tattoo without a bit of work)
C.Don't be afraid to see a few places until you find one you feel happy with. It's going to be with you for a long time so make sure it's done by someone you are happy with.
as an example I've just had some major cover up work done and although there are loads of tattoo studios near me, having talked to them and seen their work I wouldn't trust them to do a painting by numbers. I ended using a brilliant studio about 50 miles away and it's been worth the time to find them as they have been fantastic over the 20 odd hours so far getting inked with them.
most important thing......Bepanthen is your friend, forget tattoo goo or other healing creams.