Drafting is the essence of group cycling, but many riders don't do it as well as they could. Here's a technique that'll help change that.
Ride with two or more friends at a moderate pace on a safe road. Form a paceline with you in the middle, about three feet behind a rear wheel.
After you get comfortable, move closer. At two feet you'll feel a stronger slipstream. At one foot, stronger yet. That's the idea. Closer is better for energy savings. But it also requires more concentration.
If you let your attention wander, you might suddenly find yourself too close. If wheels touch, your friend will feel a slight bump but you could be in a heap. It takes better bike-handling skills than most of us have to stay up after front-wheel contact.
The instinctive reaction is to grab the brakes when you see the gap closing to mere inches. But that's the wrong way. Braking should be the last resort in a paceline or anytime someone is close behind. It slows you too abruptly and might cause them to do what you're trying to avoid -- hit a rear wheel.
Instead, soft pedal.
This is the art of continuing to turn the crank but slowly enough so you aren't applying power. You're coasting but it doesn't look like it. This should temper your speed just enough. As soon as you drift back to your margin of comfort, begin reapplying pedal pressure to maintain the gap.
Soft pedaling makes you much smoother than alternating coasting and pedaling. Suddenly stopping and starting is a sure way to annoy your riding partners, too. When everyone in a paceline is always turning their cranks, it's a beautiful thing.
Two other non-braking tips:
Sit up. As you soft pedal, this helps you catch more air to reduce speed.
Move slightly left or right. Two benefits: It slows you quicker by putting you slightly out of the slipstream, and it makes sure wheels won't touch. Do it smoothly and minimally for the safety of riders behind. Then flow back in line and resume normal pedaling.