Most piercing parlors can be infection havens, make sure the person piercing you washes his or her hands. Find some place else. Make sure they use new, sterile needles every time. Tell them you want to see them open the package the needle comes in. Pick the right kind of jewelry.
Rings are better for ears and other body parts.
Take if from someone who knows about holes, belly-button infections are gross. Follow the instructions the pierce gives you and see someone if it starts looking funny. Trust me, you won't want the earring there forever.