When hitting a shot that curves gently, such as a fade (left-to-right) or draw (right-to-left), it’s best to take your normal grip and adjust the alignment of the body and clubface to produce the desired result.
But if you need to really bend the ball to get around trees or other obstacles – think of Bubba Watson’s playoff-clinching shot at the 2012 Masters -- consider altering your grip just a touch.
To hit a hard, right-to-left hook, rotate your hands to the right on the grip until you can see at least three knuckles on the back of your left hand. This “strong” grip position will promote a free release or rolling of the hands and forearms through the ball, closing the clubface and imparting lots of sidespin.
To hit an intentional slice, rotate the hands to the left so that only one knuckle is visible on your left hand. This “weak” grip will inhibit your release, keeping the clubface open for the left-to-right spin you’re after.