Slowing a motorcycle is accomplished by increasing the drag on the front and rear wheel. Drag can be increased by allowing the engine's natural drag to transfer to the rear wheel (through deceleration and downshifting) and by applying the front and rear brakes.
Engine drag is best used when only moderate slowing is required or on long downhills where the brakes can overheat. Four-stroke engines are not harmed by this action. Two-strokes, however, should only be used in this manner for very short periods if not equipped with a decompression valve.
There is international disagreement about how to brake in an emergency. Some countries teach that you apply the rear brake first to stretch and lower the suspension. The U.S. method is to apply the front brake just a quarter count before the rear wheel. Slowly reduce pressure as you come to a stop. The direction of force when braking increases front tire grip, so the front brake has about 70% of the total stopping power of the motorcycle.
Don't lock up either wheel. Locking a wheel can be a major emergency on a motorcycle. The proper reaction to a front wheel lockup is totally different from a rear wheel lockup. Locking the front wheel reduces the bike's navigation capacity to zero. If the front wheel locks, instantly disengage and re-engage the brake quickly and repeatedly.
A rear wheel lockup is more common and not nearly as dangerous as it may seem. The tail of the bike will fishtail left and right when the rear tire is locked. Ride it out. A firm grip on the handlebars will allow you to keep the bike under control and in a straight line. Do not release the rear brake! Releasing the rear brake frees the rear wheel to roll. The rear wheel will roll in the direction it faces, which, during fishtailing, most likely is not in the same direction as the front wheel. The bike will jackknife, sending the motorcycle end-over-end.
Locking a wheel is more common in a turn since less traction reserve is available for stopping. There are also fewer opportunities to make corrective action while turning, so a lockup is extremely dangerous. Be cautious when braking during a turn. Avoid braking while swerving. Brake immediately before and after a swerve.
Braking with only the rear wheel may be necessary under certain conditions. For example, when the front wheel is not straight, applying the front brake may cause the front wheel to skid. Another example is when loose gravel covers the road but you must slow rapidly.