From Health magazine
Ease into running—and double your calorie burn—with this streamlined plan.

Getting started. Warm up your joints and muscles before each running session with an easy 3 to 5 minute walk. Do each workout below 3 times per week for at least 3 weeks before progressing to the next level. Listen to your body: Moving on before youre ready can cause aches and pains.

Weeks 1 through 3. After every 3 to 5 minutes of walking, run for 30 seconds to 2 minutes; repeat for a total of 30 minutes. Not into numbers? Run until youre tired, then walk until youre bored.

Weeks 4 through 6. Alternate 3-minute stretches of walking and running for a total of 30 minutes. If that leaves you winded, try cutting the intervals to 90 seconds, then gradually build up your time.

Weeks 7 through 9. Alternate running for 4 to 5 minutes with walking for 1–2 minutes; repeat for a total of 30 minutes.

Weeks 10 through 12. Run for 8 to 10 minutes, then walk for 1 to 2 minutes; repeat for a total of 30 minutes. Or run 1 mile, then walk for 2 minutes; repeat 3 times.

Week 13 and beyond.
Try to run 30 minutes straight. If you have to take a midrun breather, dont despair. Keep trying, and soon youll be sailing through your run, no walk breaks needed!