Great Article from motorcycle.com
Beginning riders are taught in the Motorcycle Safety Foundation (MSF) courses that effective braking is accomplished by using both front and rear brakes together. There is nothing to fear in using the front brake.
Most modern motorcycles have rear disc brakes. These brakes stop faster, wear longer, and won't fade as much. The rear disc brakes are controlled by the brake pedal.
Beginners often rely only on the rear brake since they can easily activate it using their right foot. Many have been erroneously taught that the front brake, activated by the right hand brake lever (shown here), is to be avoided.
However, remember that more than 70 percent of the stopping power of a bike is in the front brake. Get used to using the front brake and the rear brake together. As you progress in your training, you will learn how to use both the front and rear brakes to make fast controlled stops. There are also special situations where different uses of the front and rear brakes are required. When you attend the MSF classes, these situations will be covered.
Since many beginners use the rear brake too much, they often lock them up during panic situations and skid the rear tire. Remember that if you find yourself in a rear wheel skid, DO NOT release the brake pedal. Ride it out. Releasing the pedal will often cause a high side incident. This is the opposite of the advice given for a front-wheel skid with the front brake locked up (release the front brake).