Eat a full meal consisting of sugars and carbs about an hour before you are actually tattooed (about 1/2 hour before walking in), to raise your blood sugar. Bring a soda and/or candy bar just in case. Don't drink alcohol the night before, nor take asprin or blood thinners, and be well hydrated - don't overdo it though, as it will cause increased blood volume, meaning increased bleeding. This will keep you from fainting.
As for pain, while I agree that it is simply part of the process, but some people have medical reasons that cause them hypersensitivity - sometimes seen when tattooing over areas that have had liposuction. You can often have your doctor prescribe Emla cream, a strong lidocaine cream which is applied to the area about 1-2 hours in advance in a thick coat (not rubbed in) and then covered with plastic wrap. Even I've been a piercer forever, I have a thing about veins, and years ago was very ill, regularly needing IV shunts put in my arms, and Emla as the only thing that saved the doctor's office/hospital from my incessant bitching and whining. You could have put a knife through my arm and I wouldn't have felt it.
The only problem is that in some cases it makes the skin so tight that the ink won't take in the skin - it can be like tattooing plastic. Ask your doctor about it, and make sure to let the artist know also. The artist should know immediately after starting if it's not going to take.