I ran track on high school and then didn't exercise again for about 15 years. I started running again in my early thirties. I got into it to the point of hiring a running coach who has ran in 5 olympic trials. Here are some things he told me.
1) 6 - 8 weeks for building a base initially. Run slowly to build up an endurance. Just run/walk at whatever speed for 45 - 60 minutes 5 or 6 times a week.
2) Don't increase your workout by more than 10% every 2 weeks.
3) If you miss a day, you can double up two runs the following day.
The following has my schedule, but adjust accordingly because I had been "training for my training" so I was already in somewhat decent shape. He also suggested running a mile as warm up followed by 10 minutes of stretching. He also stretched at the end of each run.
Mon - 5 miles
Tue - 6 miles
Wed - 7 miles
Thu - 4 miles
Fri - 5 miles
Sat - "track day", bunch of sprints from 100 meters - 800 meters
Sun - rest
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