Jack up the mileage a little this winter, get up to 25 - 30. Once a week do a workout like this one:
-Warmup with a 2 mile jog to a track
-Run 2 miles on the track sprinting the straights and jogging the curves (sprinting means your 1 mile race pace)
-Jog 1 mile to cool down
-If you don't have access to a track you can do this workout on the road by alternating sprinting to a telephone pole then jogging to the next pole.
Take off 1 day a week and do push-ups and ab work to strengthen your upper body
In the spring run track, take a week off after track season.
In the summer, jack up the mileage again. Get up to 32 - 40 per week, and build up your long run to 8 miles.
Once a week do a hill workout where you're sprinting up a 50 - 100 yard hill 10 to 12 times (more for a shorter hill). Try to do it on a grass hill if you can find one. Jog down the hill. Jog a 2 mile warmup and a 1 to 2 mile cooldown. Once every 2 weeks do the track workout that you did in the winter. Have one day a week where you run no more than 2 miles easy. Continue doing pushups and ab work.
Good luck and let us know how it's going.