If you're a young person, don't step into a tattoo parlor unless you're certain you've stopped growing. Some folks keep maturing until their early 20s. If you're 17 and think it'll be fun to get a tattoo, keep in mind that it may not look quite right after you gain a couple of inches.
If you don't already have your heart set on a specific tattoo design, the tattoo parlor you choose should be a good source of inspiration. Most tattoo artists have at least one wall where you can view their designs, and have a lot of fun while you're doing it.