I've had my lip pierced three different times. The first time I took it out and left it for too long, and the hole closed. Second time I had it pierced right over the same spot, it hurt more due to the scar tissue, and gave me a handful of problems not healing right, so I took it out. The third time I had my lip done I had two done on the same side, one on either side of the hole from the first and second times, and they healed wonderfully. I would highly suggest moving about a centi-meter away from the spot you had it pierced before. Piercing over scar tissue will also give you more of a change to develop bad scaring, which is pretty much balls of tissue on the hole inside your mouth, and are not fun. Good luck!
I love piercings.