I have six tattoos, one of which was two and a half hours of outlining alone. The final piece totaled about five hours in the tattoo chair. Shading is far easier to take than outlining, as it's done with a needle that has three prongs and much finer points. It does hurt, sort of, but I guarantee you've experienced worse pain.
Go to a lot of shops and talk to a lot of artists. Ask for portfolios and references. Ask about how they clean their equipment. Needles should be single-use. Does the shop look and smell clean and sterile? It should. Do they have sheets they give out detailing after care? Do they do custom artwork, or only flash? (The stuff you see posted all over the walls in tattoo places). I would be cautious of a place that does only flash; I would question the skill of the artists. Also, flash art is mass-produced and frequently it's repeatedly sold, so there could be dozens of people out there with the exact same artwork on them as you.
Someone above mentioned that if you see a tattoo you like on someone, to ask them where they got it. Most people like to talk about their ink. Also, I might add if you see a tattoo that looks awful on someone, ask them, too, so you know where to NOT go.
No alcohol or aspirin 24 hours before getting inked; it thins your blood and you will bleed out more ink, draw out the process and get an inferior result after the healing.
I have tattoos on my shoulder blade, calf, three on one forearm and one around my wrist. I didn't find any of them more painful than the others, but the one on my calf comes up along the side of my knee and that place was a little more irritating, I guess. I certainly wouldn't describe the pain as agonizing or excruciating or terrible or potentially fatal. I think I might use the words annoying or irritating, but I am good at tolerating pain. It's itchy and pinchy and to me I'd describe it more as discomfort than pain. Halfway through both the first and second ones on my forearm, I nodded off.