In addition to the type of grip you choose, another characteristic of a sound grip is light grip pressure. Gripping the club too tight can cause thin, weak shots that slice. A lighter grip enhances wrist hinge - a vital power source in the swing. This light pressure also increases the amount of clubface rotation, thus improving your chance of squaring the club at impact.
On a scale of 1 to 10, where 1 is light and 10 is tight, I recommend a pressure of 4 or 5. This allows the club to be swung with power and control. At address, feel relaxed and tension-free in your hands and forearms.
Sam Snead said, "Hold the club as if you had a little baby bird in your hand." This pressure, combined with the proper placement of the hands on the handle, will give you your greatest chance to produce longer, straighter shots.

