Another area where we often see riders becoming too stiff is with their arms, especially during braking. Because you're forced to support a lot of body weight with your arms during hard braking, a natural tendency is to try and lock your elbows to help support the weight. The problem is that any bumps you encounter during braking will transfer directly into your upper body, not only making it difficult to maintain control but also unintentionally creating more steering inputs during a time when the front suspension is heavily loaded. Locking your arms also makes it difficult to change your body position if necessary for an upcoming turn while braking. Try to keep your elbows slightly bent, so that you remain flexible to help absorb any big hits and change body position if required.
It's a mantra constantly stressed at virtually every riding school you'll attend around the country: The smoother you are, the faster you'll go. This is why suspension setup is so important; if you're fighting the bike and feeding unnecessary inputs into the chassis, any instability in the bike will only get worse, and the slower you'll go. It's also a reminder of why staying relaxed even while riding aggressively helps immensely as speeds increase. In effect, the rider becomes the bike's "second" suspension, helping to soak up bumps that get past the "real" suspension, instead of becoming an additional input that only adds to the suspension's already difficult job of absorbing the energy created by hitting rough pavement at speed.
A common recommendation is to ride with the balls of your feet (the front portion just behind your toes) on the footpegs, because it's easier to change seating position. You can use this positioning to your advantage when encountering rough pavement by using your legs to take some of your weight off the seat; basically, raising your butt up just a bit so that your legs help absorb some of the bumps, and your body doesn't become additional "unsprung" weight. You'll be amazed at how much this helps the bike's stability. Obviously, this requires good leg muscle strength and can't be done for long periods (performing leg squats helps build endurance in this area), and it can't be done while hanging off through a turn at a racetrack (although your legs do provide the same effect when in this position).
A common cause of tankslappers is leaning back from acceleration and becoming too stiff in the upper body due to using the bars to support your weight; a death grip on the bars feeds additional inputs into the front end that can upset the steering geometry's self-centering balance over rough pavement. Here is where the off-road method of gripping the tank with your legs can help keep your upper body flexible by using your leg and abdominal muscles to support your weight instead of your arms. This allows you to make body positioning adjustments without putting excess pressure on the bars, as well as keeping your weight forward to help load the front end under accel-eration. Your legs are also more prepared to handle any sudden bumps that may occur.