Interval training is great for gaining speed and endurance. It is a very intense workout that will get you into great shape. Below are charts for different types of interval workouts. There are workouts for beginners (easier workouts with less distance), intermediates (moderate workouts with middle distances), and for those of us who are in great shape already (harder workouts with longer distances). The bar at the bottom of each chart indicates which workouts are geared towards speed, and those that are geared towards endurance.

Interval workouts are meant to be done on the track. 400 meters is a full lap, and 4 laps around the track is a mile. Each table is a seperate workout. The left hand column in each table is the distance to be run, while the right hand column explains how fast (or slow) to run it. The percentages mean how fast you should run compared with a full sprint (so 50% means run about half as fast as you would be running at a full sprint).