Much like a fingernail of a human, a rabbit’s nail has a pink flesh-color that runs down the middle of the nail that should not be cut. This flesh-color part of the nail is called the "quick" and it actually is a vein. As the nail grows longer, so will the quick. Be sure to trim just past the end of the quick. Having a good source of light is crucial to seeing where the quick is on your bun. If you have a rabbit with dark nails, it sometimes helps to have a flashlight handy as well as a helper to aid you in where you should cut.

If you have a rabbit that doesn't like to sit still, you can use your towel to swaddle him/her up. This is actually a really nice method to practice, for it helps you to pull out and concentrate on one foot at a time.
Even the most skilled nail trimmers make mistakes and accidentally cut the quick. In this case it is a really good idea to use cotton/bandages and apply small pressure to the wound. Make sure the bleeding stops before you leave your rabbit unattended in its cage.
It is usually a good idea to trim your bunny's nails every 3 weeks. The more you trim your pet's nails, the more you and your pet will become comfortable with this procedure.