This is all shit they'll go over when you're done (or before)
You'll have a bandage over the tattoo which which will be able to come off after 1-2 hours (may vary on size? not sure but thats how it was for my tats.) After that you'll wash it lightly with a little soap and warm water. You'll see some of the color look like its bleeding off after: this is natural, dont panic (excess ink). Again, gentle with the soap and water. Pat the area dry very lightly after washing. After that, I used A+D ointment over the tat, a very light coating of it.
http://img.walgreens.com/dbimagecach..._220x220_a.jpg
You will do this about 4 times a day for the first 3-4 days after getting the tat. After that you wont need the soap and water anymore aside from your regular washing routing (unless you're a dirty bastard?) Keep using the A+D ointment around 4 times a day for the first week or so. After that I would still use the ointment once in the morning and again before i go to bed for about another 2 weeks.
For during, just relax is the best advice I can give. Try to have a little something in your stomach beforehand. The place I went to a few times lets you put your ipod into a dock to listen to music while its getting done, helps to relax. The pain is not bad, its a mild annoyance. I honestly dont think 'flexing' would be much of a problem. The more painful tats are ones that get done closer to the bone, like around the wrists or on the tops of your feet (only tats I've seen done that looked painful, my exgf got stuff done to the tops of her feet which she was in agonizing pain for, although she may have been a wimp) The pec area shouldnt be too painful I imagine.