I say this a lot, but it doesn't usually sink in. A major reason for tired hands, sore wrists, numb hands, etc is because riders hold into handlebars with death grips. Your hands should be very loose on the bars. Your grip should only be strong enough to twist the throttle and you should bear no weight on the bars...even when braking. The safe connection points you should have on your bike are at you legs, knees, feet, ankles, elbows on tank, stomach on tank, etc.
If you are experiencing hand and wrist discomfort, then read up on riding ergonomics. There is a lot to learn, and it will make you a much better rider!! Now, there is no way to always remember to keep your weight off the bars, but pay attention to it and you'll notice your hands feel better. You'll also notice the bike turns better, the suspension doesn't beat you up through your arms, and the bike is much smoother and more stable in turns.
FYI, keeping weight off your bars when braking may also save you from crashing. A major cause of crashes is weight on the bars during a front wheel slide. If you have no weight on your bars, then the tire just slides and you'll likely keep the bike upright. If you have weight on the bars, then you WILL turn the wheel and potentially endo.