Being able to stop suddenly in a short distance can get you out of big trouble. Learn this skill with a few minutes of practice on a quiet stretch of pavement. Here's how:
Pedal up to a decent speed. About 15 mph is enough.
Stop pedaling with the crankarms horizontal.
Extend your arms to push your body back as you grab the brake levers. Let your butt go off the rear of the saddle, putting you in a long, low position over the bike.
Squeeze the front brake harder to stop faster. Maximum stopping power is in the front wheel as weight shifts forward. Having your body low and rearward prevents tipping over the handlebar.
Squeeze the rear brake a little less to prevent the tire from skidding. Of course, in a real panic stop this is a low priority.
Be very careful as you practice! This technique is meant to prevent crashes, not cause them. Always keep the bike on a straight like. Trying to stop like this while turning could easily make you lose control.
Once you've added panic stops to your bag of tricks, you'll do the right thing when a car, dog or freight train suddenly appears out of nowhere.