first you must learn how to stop the rear wheel...

1) put your weight as far forward as you can. (this makes it easier to stop the rear wheel)

imagine a clock face on your drive side

2) when your stronger leg is at about 7 o clock, start pushing down hard on the pedal with that leg

3) simultaneously pull up on your weak leg's pedal to help your strong foot stop.

the goal is to have your strong foot stop between 9 and 10 o clock

if you're having problems, try going a little slower...

after that you can worry about keeping the wheel steady and distance, which come with practice