Cardio is important too, you know.
Run for time-
Easy – 2-4KM
Normal – 5-7KM
Hard – 8-10KM
If you have a course you run often, use it and time yourself. The goal is speed, not time spent running. I currently run two separate courses (semi) regularly, one near my house (4KM) and one near my work (3.6KM) to beat my past time each attempt.
Running is one of my Achilles Heals: I am a very slow runner, though I have found that if I keep up with it regularly my times decrease.