The only purpose of the bridge hand is to provide a stable path for the cue stick to travel while striking the cue ball. Do not lean on it to suppot your body--let your stance carry your weight.
hand, and not just your fingers, be on the table surface or rail. Resting your fingertips on the table to form a bridge is unstable and should be avoided. Not only is a raised bridge unstable, but it also requires you to elevate the back end of your cue; contact with the cue ball is always best when your cue is as level to the table as possible.There are times when you can't avoid using just your fingers, like when you must shoot over a ball and have to raise your bridge above it. These type of shots are much harder to execute and reinforces the need to keep your hand on the table. Practice these shots to find the most stable position of your fingers. Sometimes it is more stable with your finger tips spread out as far as possible. At other times you may want your fingers tight together in a group. In every shot, you want your bridge hand as stable as it can possibly be. Should I use an open bridge or a closed bridge? If you are shooting a shot with extreme english or shooting harder than usual, you will want to use a closed bridge. In most other cases, just choose whichever is more comfortable. If both feel the same, keep in mind that an open bridge allows you to see the cue ball better.
The bottom line: create the most stable bridge you can, while keeping your cue as level to the table as possible.