having a clean body is actually an important one that most people don't think about, especially FEET. Vicks Vapor rub under your nostrils only does so much. With that being said, I have seen the problem of people wearing too much perfume/cologne. Not everyone likes the smells but especially for people that have to work so close to you! Be open to the fact that the tattooer is not just a tattooer, but an artist. It is more gratifying when the artist can somewhat manipulate what you want into their own creation. I'm not saying an artist should completely alter the tattoo, but not only is it on your body but it is a representation of the artist that worked hard on the drawing & tattoo for you. It is their artwork. Another huge thing that I have learned in this industry is that it is awesome to bring in pictures of what you are looking to get done, it gives the artist a little peak into your brain & what you are picturing BUT the WORST is when people bring in pictures of other tattoos. You can't do anything with that. A reference as far as style or color or something is sometimes okay, but to bring in a picture of someone else's tattoo makes it really difficult for the artist to work off of. Real life pictures are always the best & from there you can change things however you wish.
If you aren't sure how to tip accordingly, ask around before you get to that point. A lot of artists pay booth rentals or only get a percentage of the actual cost of tattoo, along with purchasing their own equipment & supplies so they live off of tips. I've always stuck to asking other artists rather then just tattooed friends.
Always bring your ID. Most shops don't keep information on file, they have it stored away for legal purposes.
Best tip I have ever been given "get what you want & not what you can afford." If you are quoted $500 for the piece you went into detail describing, then save up, otherwise you WILL get what you pay for & you have to live with that. I have seen so many people say things like "well what if I get it this way, will it be cheaper?" to the point where I wouldn't be surprised to hear "I want an angel..." (price given) "what if I just get it with 1 wing?"
Those are some major tips I try to pass along to customers & friends. Hope this helps!