Lining up the vermillion border
We all know the importance of lining up the two sides of a laceration that goes through the vermillion border of a lip laceration. Injecting lidocaine or swelling from the trauma itself can make this difficult. Use a skin marker to outline the the vermillion border on each side, making this easier.
This photo comes from this great tutorial on Closing the Gap
For lip lacerations requiring repair beyond simple alignment, consult a plastic surgeon. Here is an interesting discussion on Plastic Surgery Key