Another important piece of information to know is a vast majority of tattoo artist will let their repeat customers make an appointment so they don't have to wait around. Ask your artist if they could do this for you as well. Also keep in mind that most tattoo parlors don't have a huge waiting line so you don't have to worry about that. The only time this could be a problem is if you are visiting a very popular tattoo parlor like Miami Ink, LA, Ink or Carey Hart's tattoo or studio in Las Vegas Hart & Huntington or any tattoo parlor that celebrities like to hang out at and get inked.
Another good piece of information to know is that some tattoo artist charge by the hour and some charge by size, design, how much ink is being used or amount of detail the tattoo has. You just have to ask your particular artist to see which method they follow and always remember to tip your tattoo artist.