Stay off your rear brake, unless you use it in conjunction with your front. I'll spare you the geometry/physics lesson.
(However, it DOES help to trail brake just a bit with the rear when you're turning tight in parking lots.)

 

the front brake is your main braking force...like Jeffzx9 said use the rear in conjuction with...you lock up that rear and start sliding you just lost control of your bike...

 

Thansk guys. I wassss using it in conjunction with my front brake. I was braking with 70% front and 30% rear. It seemed to be working well. Plus that book called proficient motorcycling written by david hough suggested that I get in the habit of using both brakes at the same time.