I don't have a fool-proof summer training plan I can give you because I don't know your background very well but I can give you pointers. Generally you want to take about 2 weeks off from training after track season and then start with lower mileage (25-30ish). Every week or to you should add 5-10 miles to your weekly mileage until reach your peak in late July/early August and then you might want to take a week of lower mileage before the season starts. You should not only be building base though, you also want to be doing other stuff like tempos, fartleks, striders, and definitely long runs. A solid week in the middle of summer should look something like this:
Monday: Maintance run with core afterwards (~8 miles)
Tuesday: Run with a 2-3 mile tempo in the middle (~9 miles)
Wednesday: Maintance run with core afterwards (~8 miles)
Thursday: Maintance run with 200m striders on a track (~8 miles)
Friday: Run with a 15-20 minute Farlek in the middle with core afterwards (~9 miles)
Saturday: Recovery run (~6 miles)
Sunday: Long Run (~12 miles)
You can adjust the exact mileage totals but generally most good high schoolers are running like 50-70 mpw as their highest total in early August. You can find other good plans by just using google (Jay Johnson and Jack Daniels have some good ones). But for the most part those are just the ingredients and its up to you (and your coach) to figure out the best recipe for you. You can take a few days off and run twice in one day (affectionately known as doubling) too but you want to be careful with that stuff because too much of either can be bad. Lastly here is a good link that also talks about summer training:
http://www.runnersworld.com/rt-web-exclusive/summer-training-for-high-school-runners
Good luck and happy running!