Intraval- to run a series of relatively short repetitions over various distances from with rest periods of slower running in between. The 200 meters is best for short-distance training (5K and under) to improve speed. The 400 meters helps improve overall conditioning at slower paces, and at faster paces is good final race preparation. The 800 meters is used to develop speed when training for races 10K and under and to condition form and pace when training for longer races. The mile is used most often to train for longer races, from 10K to marathon, to help improve pace judgment and overall conditioning.
Hills - the idea of hill work is to negotiate the hills efficiently, with as little disruption as possible to your rhythm. Think of yourself rolling over the hill, almost as if it isn't there. Concentrate on keeping your upper body relaxed, while you let your legs do the work. On gradual inclines, try to run a bit harder than you had been running on the flat before the hill. On steeper inclines, concentrate on lifting your knees and pushing off hard with every step.
Fartlek - gets your legs used to a variety of paces and in the process gives you an enhanced awareness of your ability to keep up those paces at various distances. Vary the speed and times of the speed sections, from as short as 15 seconds to as long as two or three minutes.
Tempo Runs - call for a single sustained effort. The result is that your body learns race economy: running at a fast pace for relatively long periods of time. Tempo runs will give your top speed a boost, too. By running nearly at race pace, your body becomes accustomed to running close to its upper limit (though not exceeding it). In doing so, you actually increase that upper limit, and you become gradually faster.