The key is finding your current level of fitness. Using a good recent race performance to do this, and plus the numbers into the McMillan Running Calculator. This will provide a helpful range of paces for virtually every type of workout you can imagine.
Long Runs : The most essential, but often the most misunderstood, component of your training schedule. Most weeks should include a long run of at least 90 minutes. Advice on how hard to run these varies somewhat, but most successful runners run these at two to two-and-one-half minutes slower than 10K pace, or 60-90 seconds slower than marathon pace. That can seem quite slow at times, but the purpose of these runs is not to build speed or wear yourself out by a hard pace. (As you build distance, that will make you tired enough). It can take great discipline to keep these runs at the desired pace. Another way to measure the right effort is heart rate: about 70 percent of maximum heart rate is just about right. This can mean an even slower pace in the hot summer months.
Towards the end of a training cycle, when you are approaching your "peak," some of your long runs should include a significant stretch at your marathon pace (40-60 seconds slower than 10K pace) or a shorter stretch (20 minutes, or 2 x 15 minutes) at tempo pace.
Don't overdo the distance of your long runs, even when training for a marathon. Multiple 20-milers tend to prove out the law of diminishing returns. For most marathoners, a series of gradually longer runs during the 4 to 5 months preceding the marathon, with the 6 to 8 longest runs averaging 16-18 miles, will be sufficient. The key is time on your feet, not distance. Coaching guru Dr. Jack Daniels, for example, recommends a long run of not more than 2 hours and 30 minutes.
Tempo Runs : The next most important part of training. We spend much of the winter training at tempo pace. If you really raced Cherry Blossom, or will really race an upcoming 15K, you will know your "tempo pace": it is your pace in that race.
Tempo and Cruise Intervals: We run a variety of tempo-and ?cruise?-paced workouts. Tempo intervals are run at just slightly faster than 10M race pace, while ?cruise? intervals are done at close to 10K race pace. Recovery intervals are short. Again, the McMillan calculator will give you precise pace ranges for these types of workouts.
Interval Workouts : Repeats from 400M to 5:00 in length, run at 5K pace, with a long break for longer repeats, and shorter breaks for shorter repeats.
"Faster" Interval Workouts : These are shorter distances, usually 400M or less, run at 3K pace, Mile pace, or faster. If done at 3K pace, a jogged 1-minute recovery is enough. As you get faster, a longer recovery is needed. We do relatively few of these workouts on Wednesday night, but they can be used as a second speed workout in the late summer and fall to complement our Wednesday night efforts. But these should be "short" workouts, covering no more than 2 miles in total repeat distance.