I picked up this tip somewhere long ago and it made a major difference in my ride enjoyment.
Lay your fingers on the grips slightly wrapped around and do so as if your fingers had glue on the or were sticky. You don't need to wrap your fingers and hands tightly around the grips. Practice this and you will be surprised at how little effort is required to maintain control.
Of course if you are in city traffic, etc. you should slightly tighten up your grip to allow better control/adjustments to outside environment, cages, kids, car doors, etc.
Great site great tips.