How do i get a better mile time?

What lowered my time was running long distances making the mile seem short. I'm also in track, short distance though because I want to get faster, and my coach send the long distance group out on long runs. He also has them run a mile or two miles going fast for one lap and the "slow" the next and then fast again. He's a good coach and knows what he is doing so my guess is that is a good workout.