I always seem to manage to get a bit of a cat-nap in somewhere along the way.
I certainly like a good quality, long nights sleep before hand, and very definitely for a few nights afterwards. Avoid alcohol before having it done, and keep topped up with water / simple good quality food during the session.
Ask for a bit of a break if you need one rather than fidget / get stiff – I always ask my tattooist if he’d like a quick bit of a break too if he looks like he needs one, or has been going a while.
Going over my collar bone was the only place that caused me to jump a bit, my ribs / elbows seemed to be ok?
I could be making this up, but I don’t know that caffeinated drinks are a good idea immediately before / during either (are they?).