Summarize the following:
Over a period of time, interval training increases how fast you can run by forcing you to use muscles at a higher capacity.  Begin running at a steady pace. Increase your speed for a particular interval. You can use distance markers on a track or a timer if you're running through a neighborhood. Keep the increases short, at about 20 seconds or so. Once you are at your top speed, slow back down. Repeat as you're able, increasing the number per workout over time. Similar to strides, you increase your speed for short bursts. However, instead of doing it at regular intervals, you do it as you feel moved to do so. Also, you can add in other movements, such as jumping or bounding instead of running more quickly.  To try fartlek, increase your speed as you feel like it while running. Go up to your top speed, and then decrease down again. Alternatively, switch to hopping or bouncing instead. Keep these bursts at less than a minute. Like strides, fartlek can increase your overall speed by stretching your capacity in short bursts. Going uphill helps keep you in proper running form. It forces you to pick your knees and feet up and makes you use your arms to help move yourself upward. Running uphill also builds your muscles, as you're fighting against gravity.  Choose a road or hill with a slight incline. You should be able to go back downhill when you are in the recovery stage of your workout. Increase your speed in short bursts. Go faster for short periods, keeping it under a minute for each interval. Use the down slope for recovery. Once you've made it up the hill, gently jog down the hill for recovery. Hill intervals can increase speed, as they improve technique, increase strength, and push your capacity to make you go faster.

Summary:
Use stride interval training. For variety, try fartlek. Increase intensity with hill intervals.