Please let your vet do it. If possible have them do the clamp and twist method, this will cause less pain, less blood and less chances of an infection.
Please don't use the rubberband method, it is way more painful for them and it doesn't come out as neat and chances for an infection are alot greater. My cocker had her tail docked using the band method when I got her from a breeder. And like Lacy's mom predicted, her tail is calloused and bald on the tip, no hair will grow on the tip of it. She is also very sensitive about it being touched, I feel really bad that she had to have it done this way.
You can tell the difference between a dog's tail that is docked by the vet properly versus using the band method.