* Don't be ashamed of your budget: It's cool to be upfront about your budget and ask what the artist can do in that budget (if reasonable). I had a friend who wanted so badly to get tattooed at last year's Empire State Convention as a souvenir of his first show, but only had $150. He wanted an Americana piece and approached artists who were doing walk-up flash to see if he can get anything for what he could afford. I watched the first artist he approached (in a respectful way) be a total dick and scoff at doing anything for that budget. [I won't name the artist but I will never recommend him again.] Convention booths are very expensive, so it is completely reasonable for artists to have a minimum to make up the costs of the show (and travel, etc). Not reasonable, however, to be an asshole about it. My friend eventually found a great artist to work within his budget and has gone back to the same artist for more work since.
* Don't expect the drawing in advance of your appointment: As Demetra writes on the design process, "Some artists will prefer to do a pre-drawing and use a stencil, others might free hand a design directly on skin with markers." It's natural to want a peak of your custom design if the artist will be sketching out your work in advance of the appointment, but many artists will not email or hand you the design prior to meeting and that's because there are too many shady people who will pay a small deposit, have a top artist design the tattoo, and then they'll cancel the actual tattoo appointment and bring the design to a cheaper artist. Who would do such a thing? LOTS! In fact, I know first hand of one tattooer who did it to another (for a facial tattoo!). So keep that in mind if you're asked to wait until the convention to get a look at the design.
* Don't be drunk at your appointment. Demetra mentions the No Booze rule for clients. I'm mentioning it for artists. I was once told, "Tattoo conventions are the best places to get the worst tattoos by the best artists." And that can be very true. Conventions are a party. That's why I love them. But if someone is throwing down a lot of cash to get tattooed by you, at least wait to go wild at the final after-party when there's no work the next day. Of course, if you're in the hotel room giving each other free drunken tattoos, well, then you're clear, ethically.
* Don't come with your squad. Despite being expensive for artists, convention booths are often really small and can barely accommodate you, the artist and supplies. They cannot accommodate your crew. Roll twenty deep at the club later on.
* Don't let your Selfie Stick come between you and the tattoo. Your primary goal is to get a good tattoo, not more Snapchat followers. Save your rainbow puke filters until after your session.
* Don't be too serious. You're getting a tattoo! Yeah! Don't worry about being too cool, too tough, too artsy, too whatever. Enjoy the process and also enjoy the show. Smile. Make friends. Make eye contact with that cutie. Maybe you'll take something more than a tattoo home.