If you don't have all day to train, this is the way to do it for optimal results.
#1 Run as many miles as you can without getting injured. You don't need a to do many workouts, just a tempo-run and fartlek every week.
#2 If you are injury prone cross train a lot. (As long as you don't have a major race around the corner.) Biking, elliptical, rowing, aqua jogging, etc. The more volume you can do, the fitter you will become.
#3 Lifting, stretching, ab exercises, etc are overrated. These things are good to do but your time would be much better spent cross training.