These Four Principles should be part of your training plan throughout the year. Tailor them according to your goals, interests and needs.
You don't need to run every day, but be sure to run more days that you don't.
At least once a week inject speed into your routine. For example, perform four - to five-mile tempo runs or long intervals at 5-K race pace. Mix up repeats by running 4 x 1 mile one week, 5 x 1200 meters another, and 3 x 2000 meters another.
Follow hard workouts with at least one easy day and don't worry about how fast you're going. Let your energy level be your guide.
Once a week, run 1.5 time longer than your normal run.
From Runners World magazine, January 2010