As a beginning runner, your top training priority is to establish a solid foundation for your future development as a runner. How is this done? The physiological foundation for running performance has two components: aerobic fitness and neuromuscular fitness. You know what aerobic fitness is: the ability to generate large amounts of energy efficiently with oxygen taken from the environment. Neuromuscular fitness is the ability to generate a high level of stride power in an energy-efficient manner.
When you first take up running, you need to focus your training on developing these characteristics in a manner that is appropriate for a person starting at square one. Veteran runners, who have already developed a solid foundation of aerobic and neuromuscular fitness, need to focus their training instead on advanced types of workouts that build on this foundation and on "specific-endurance" workouts that combine high aerobic and neuromuscular demands and thereby simulate race intensities.
Aerobic Training 101The best way to lay a foundation of aerobic fitness is quite simple: Perform a gradually and steadily increasing amount of running at a comfortable pace. Start by running every other day and work toward running six or seven days a week. Start with short (15 to 20-minute) runs and slowly increase the duration of your average run to 45 minutes or so. Do one "long run" per week on Saturday or Sunday. Keep increasing the duration of this run until it's long enough to carry you to the finish line of the longest events you care to do.
Total running volume is the single best predictor of running fitness. That's why the vast majority of elite runners work out twice a day and run upwards of 100 miles per week. You can improve as a runner for years simply by increasing the amount of easy running you do each week until you reach the maximum level you're comfortable with (even if it's nowhere near 100 miles per week!). Sure, you can mix in some more advanced types of aerobic training, such as threshold runs, which consist of extended segments (10 to 30 minutes) of moderately hard running between a warm-up and cool-down, but as a beginner you should keep this type of training to a minimum and prioritize sheer volume.
Neuromuscular TrainingIf the best way to build a foundation of aerobic fitness is to go long and slow, the best way to build a foundation of neuromuscular fitness is to do very short, very fast efforts such as speed intervals (e.g. 6 x 300-meter relaxed sprints a track), fartlek intervals (30-60-second hard efforts sprinkled throughout an otherwise easy run) and steep hill sprints.
Start with steep hill sprints. These short, maximum-intensity efforts against gravity provide two key benefits. First, they strengthen all of the running muscles, making you much less injury-prone. They also increase the power and efficiency of the stride, enabling you to cover more ground with each stride with less energy in race circumstances. These are significant benefits from a training method that takes very little time and is fun to do.
If you have never done a steep hill sprint before, you should not leap into a set of 10 of steep hill sprints the very first time you try them. These efforts place a tremendous stress on the muscles and connective tissues. Thus, the careless beginner is at some risk of suffering a muscle or tendon strain or another such acute injury when performing steep hill sprints. Once your legs have adapted to the stress they impose, steep hill sprints actually protect against injury. But you must proceed with caution until you get over the hump of those early adaptations.