Ease into faster running with these introductory workouts:
1. Easy fartlek. Fartlek, or speed play, is variable-pace running that emphasizes creativity. During a 30-minute run, choose objects to run to telephone poles, trees, buildings, other runners, whatever. Make choices that mark off different distances so your pickups vary in length from 15 to 90 seconds, and modify your pace to match the distance. If you're with a group, take turns choosing, sometimes revealing your choice ahead of time, sometimes not.
2. Hills. Warm up with a 10-minute run to the base of a hill that has a steady (but not overly steep) slope. Run up at a constant pace for up to 45 seconds, then jog back down and repeat four more times. Move at a speed that allows you to finish each 45-second segment without gasping. The hill will present resistance; your job is to run controlled and steady, focusing on form.
3. Strides. On a track, run quickly for about 15 seconds every time you start a straightaway, then ease off and jog the rest of the straightaway and the turn before beginning another 15-second stride. Do this for a mile or so (eight to 12 strides). You can also do strides after a run (grass fields are nice), striding for 15 seconds one way, then jogging back and repeating eight to 10 times.
4. Races (5- and 10Ks). Entering races now and then will do two things: First, it'll help you learn to run at a constant pace over a longer period of time. Second, since much training advice is based on a runner's 5- and 10K times, knowing your personal benchmarks at these distances can help you tailor your speed workouts more effectively.