When my wife got her foot done, she was laughing at a friend who had said how shitty it was. She thought he was referring to the actual pain while getting tattooed. She realized the next day how crappy the healing was. She wishes she'd done both at once (like her best friend did) to just get all of the healing/swelling/limping done at once. Of course, she is glad she has her other foot free for a Monmon cat. Follow the tips from everyone above and you'll be fine.
Hell, I had a foot injury for the better part of the last year, and I'm regretting not getting mine tattooed while I wasn't running six days a week. I may actually get them done a few days after my next marathon. I figure I'll be limping anyway, so why not?