A few workouts that you can do to increase your speed are fartlek workouts, speed workouts and hill workouts. With fartlek, which is a Swedish word for speed play, you take small, unstructured bursts of speed. You can do them for a distance or you can do them for time. With the speed play, you can have it be as long as you want to, as long as you're challenging yourself, in a different way from the regular speed that you're usually running during your runs. Speed workouts you can do on a track.
You can do quarter mile repeats, half mile repeats or mile repeats or any distance that you choose. You want to increase your speed, but that's not going to happen, if you continue to run at the same speed day after day, over the same distance. What you need to do is challenge your body in its different systems. So fartlek speed workouts and hill workouts will do that for you. You're taking short bursts of speed, challenging your body and that will make your longer runs at that same speed seem easier and help you go to a different level in your training.