If you've been running for a while and are comfortable running 3-4 miles at a stretch, you may be thinking about improving your speed. My joke is that the only way to improve speed is to run faster. That may be glib, but it’s not so far from the truth. However it’s best to break the steps into small doable pieces. These are the steps that will help you run faster.
Remember to introduce speed work safely. By running faster you are activating fast-twitch muscle fibers that may be under utilized. Doing too much speed (and distance) too soon could cause an injury. Start doing speed work in small doses. Once a week is good way to start. Always remember to warm-up and cool down by running easily for 10 minutes.
Start with Strides. Strides are 60 to 100 meter pickups. Towards the end of a comfortable run gradually accelerate to about 85% of your maximum speed. Keep this for 2/3 of the stride, and then allow yourself to decelerate over the final third. This quick pickup helps to improve your neuromuscular coordination and will allow you to increase your speed.
Follow with Fartleks. Fartleks are a series of longer pickups with a recovery in between. The term is Swedish for speed play. They are unstructured and the play aspect is key. After an easy warm-up, chose an object that is in your sight and run towards it at a faster pace, such as a mailbox, the lamppost, the playground. Once you reach the spot, slow down and allow yourself a few minutes to recover before choosing another destination. These are essentially games. One I invented I call, “Oh no you don’t.” Once I am warmed up I won’t let anyone pass me. Sometimes this is easy and a runner and I will be well matched. Sometimes the runner is much faster and it is a challenge, I will give it good go before easing up. See what games you can invent.
Intense Intervals. Interval training is a structured speed work, the distance is measure and timed. Classic interval training is around a track. After an easy warm-up, run a lap slightly faster than your normal pace. Follow by a recovery lap. And keep it going. The whole point of these is to take yourself out of your comfort zone. Once you start doing these on a regular basis, slowly increase the number of laps you run fast making sure to always keep a recovery lap or two.
Breaking down speed work into chunks will allow you to safely increase your speed. Keep doing it on a regular basis and you will start to see results. Guaranteed.