Here's what you shouldn't do: run big miles all summer (starting now), with little or no faster stuff, to "get stronger." Start from where you are--good speed, not-so-hot endurance--and build gradually and progressively from there.
Stay in touch with your *skill* of efficient running at middle-distance paces throughout the summer, but don't worry about the specific conditioning that allows you to *sustain* that pace in a race. So once every week to ten days, do a moderate amount (say 1,200 to 2,000m total) of turnover stuff, with good (close to full) recoveries between repeats.
If you're doing these on a track, 150s or 250s are good, because you probably don't have anything "invested" in running a particular time on those, and you can just let yourself run free and easy. If you're off the track, you can do a semi-structured fartlek, where you do, say, 30-60sec of that free and easy running, then follow with several minutes' easy running and/or brisk walk (I know, walking is anathema on this board) to get your breath well back.
Look up the Summer of Malmo to get some more ideas and guidance, but make your mileage buildup gradual--*don't* jump into big miles with both feet, but add mileage smoothly and progressively over the course of the whole summer. If you're doing the doubles that he recommends (as I do), start with just one or two double days per week; you can add another one every 2-4 weeks.
Especially follow his guidance about staying within yourself, throughout your summer of running. You want to get to the end of summer "full of running" and ready to *start* your specific cross-country training.
Good luck. Please bump this thread occasionally and let us know how you're doing.
Thanks for kind words.
For at least 90% of high school and college runners, I think all-one-speed summer training is a serious mistake, and an even bigger mistake for the kids who've run middle-distance races during the track season.
If people really take a look at Summer of Malmo--ALL of it--and think seriously about how to adapt it to themselves and their individual situations, I think they'll come up with more enjoyable, more "natural," and more productive summer training programs.
I do miss the days when jtupper, Jim Spivey, Ruth Wysocki et al. would stop by. They had some really helpful advice. I miss runningart2004, too--haven't seen any of his stuff about strength training for a while.
Great advice from lease. I will add that for most true MD (800-1600, not 1600-3200) types, XC will be frustrating from a competitive stand point. Just use it for conditioning and comeraderie and soak up the wards and accolades when track rolls around.
Also, hills. Lots of hills.