Your wrists must both be above the rim. If both wrists are over the rim, you will be able to dunk more successfully and easily. There will be no more contacting the rim with the basketball when attempting to dunk. It will be simple and straightforward. The more hands you can use to reach for the sky, the better. But if your goal is to learn how to do a two-handed dunk, then getting as high as possible is not recommended. The risk of injury increases as you go higher. Instead, start by learning how to do a one-handed dunk and work your way up from there.