Pretty much what everyone else said... I don't let my wheels get locked up, and I use both brakes in balance to get maximum stopping power.

A biggie that some faster riders around here don't realize tho... you need to look ahead just as far on a bike as you would in a car, or even further. You can't avoid all emergency stops that way, but it does help. Coasting a bit or using a lower cruising speed can eliminate a lot of emergencies too. Around here, some of the major arteries have light timings where the main road has long enough lights that a 15mph rider won't have to stop, and pushing to 20mph can mean a lot of sudden stops. (there are roads that are just the opposite too of course)