A lot of people like to overcomplicate training. Advanced workouts, intricate training schedules, and complex strength circuits all have their place in pushing the limits of talent and race preparation, but when it comes to the real legwork of training—getting a young, talented runner into great shape, or getting big improvements out of a less talented runner—the road to success is really pretty simple.
The following steps, in order, are the path that I believe male high school distance runners should take if they want to improve long-term. The training progression laid out below may not be ideal for running your fastest right now, but that's not the intent—the intent is to improve long-term.
The specifics of a training program are highly variable and depend on a lot of factors. That's why I'm not a huge fan of pre-packaged training plans. But despite that, there are principles that apply to nearly everyone. There will always be exceptions: if you're very talented but highly injury-prone, for example, you'd want to adopt a substantially different plan, as consistency and health is more important than peak volume. Runners with substantial speed (under 56 in the 400m for boys without very much training) would also likely adopt a schedule with more focus on developing speed. But if you're a relatively durable but average, unathletic, skinny guy, this is the roadmap you want to follow during your "off season" training—i.e. the summer and the winter.
Your off-season training is usually the part about your running where you have the most control, and it's where you'll likely make the most improvements. Another perk is that you are pretty much guaranteed some good races if your off-season training is good. While training and workouts during the racing season are obviously important, it's very hard for anything but a totally incompetent coach to screw you up too badly if you're already an aerobic monster.
Many of the same principles apply to girls, but I'm not comfortable putting down concrete paces or run distances because I just haven't coached very many of them.
The below steps should be done in order, and you should not move ahead to the next step until you're able to do the previous one. For example, if you can't run six days per week without getting injured, figure out WHY and fix it before you try to do all of your runs faster. Avoiding injury is a big subject, one which deserves its own "roadmap to success," which I'll write up some other time.
A few of these steps can be adopted simultaneously or in any order, and are noted below. Do note that it will take a long time to progress through this plan. Not "long" as in months; "long" as in years. In most cases, the year you start running six days a week will not (or should not) be the one where you start doubling four days a week and doing fifteen mile long runs. Running is for the patient—marshal your ambition!