As a person who ran out and got a tattoo as soon as she could after turning 18, let me offer a very important suggestion:
Do your research. As much as you might be in a rush to get it, a tattoo will be on you for the rest of your life, so you want to make sure it is done by someone who is skilled, careful, and patient. Make sure you've seen other tattoos they've done-- they should have a book-- and that they're high quality. Check and see if they enjoy doing the kind of tattoo you want-- you don't want someone tattooing you who is hating what they're doing the whole time. Listen to them when they give you advice about size and placement-- they know what they're talking about. If they say the size you want is too small to accommodate the detail you want,
listen. Be prepared to go a few inches bigger or choose a different design.
And of course, obey their instructions about aftercare! You don't want to get a nice tattoo and then ruin it because you decided to jump in a lake or get it dirty and infected before it could heal.
Oh, and if you like the job the artist did, and especially if you can see yourself going back to him/her....tip.
Now, after all of the precautions.....Congratulations! You are charged with the responsibility of making sure you take pictures and posting them here when you get it.