Here's a simple 30/30 plan to get you going, featuring 30 minutes of exercise for the first 30 days. It is a routine similar to one that Chuck Cornett, a coach from Orange Park, Florida, uses with beginning runners.
Walk out the door and go 15 minutes in one direction, turn around, and return 15 minutes to where you started: 30 minutes total.
For the first 10 minutes of your workout, it is obligatory that you walk: No running!
For the last 5 minutes of your workout, it is obligatory that you walk: Again, no running!
During the middle 15 minutes of the workout, you are free to jog or run--as long as you do so easily and do not push yourself.
Here's how to run during those middle 15 minutes: Jog for 30 seconds, walk until you are recovered, jog 30 seconds again. Jog, walk. Jog, walk. Jog, walk.
Once comfortable jogging and walking, adapt a 30/30 pattern: jogging 30 seconds, walking 30 seconds, etc.
Follow this 30/30 pattern for 30 days. If you train continuously (every day), you can complete this stage in a month. If you train only every other day, it will take you two months. Do what your body tells you. Everyone is different in their ability to adapt to exercise. When you're beginning, it is better to do too little than too much.
If you continue this 30/30 routine for 30 days, you will finish the month able to cover between one and two miles walking and jogging. Your next goal is to develop an ability to run continuously for a mile, then two miles, then more if you want. The way to do that is to gradually increase the length of time in the middle of your workout spent jogging and decrease the number of walking breaks. Do 45/30 (45 seconds jogging, 30 seconds walking), then 60/30, then 75/30, or 60/15.
Vary your routine. Work a little harder one day, then make the next an easy day. Program in occasional rest days when you do no walking and jogging, or cross-training days when you do some other exercise. Test yourself to see if you can run a half-mile continuously, then a mile. It won't happen overnight, but you should begin to see a gradual improvement in your physical fitness.
If the above routine seems too difficult for you, do a little less. Nobody is looking over your shoulder when you write how much exercise you did today in your diary. Only you can judge whether you are pushing too fast or too slow, but it's best to err on the conservative side.
You too can become a runner. All you need to do is begin.
Keep a log to monitor your progress!