The grip is essential to get your arms and the club working together. The swing is entirely dependent on this. There should be no tension while gripping the club. While both overlapping and interlocking grips are ok, the former is far more popular.  Tiger however uses the latter so the choice is entirely yours. 

Place the "leather" of the club in your cupped left hand so that it starts at the heel of you palm and crosses the base of your index finger. Close you fingers around the grip, placing your thumb on top of the shaft a little to the right of center. The idea for this location is that at the top of the backswing your thumb will be directly under the shaft and supporting it. The groove at the base of your fingers clamps around the club. The 'V' of your thumb and forefinger should point to your right shoulder.

Now the right hand goes on with its little finger overlapping the forefinger of the left hand for the overlapping grip. Again the channel at the base of the fingers grips the club and the 'V' points to the right shoulder. The right forefinger should be gripping the club separately and a little farther down the shaft; this enhances directional control.

When addressing the ball the palm of the right hand should face toward the target and the palms of the right and left hands should oppose each other. 

In order to get more power, the right hand may be rotated back slightly. This will generate more wrist action but there may be loss of accuracy.