High school coaches really have their hands full when confronted with the multitude of conditioning levels and needs of the athletes under their charge. Football is typically the exception, as they basically are allowed to train their kids year round. Track coaches like myself will have athletes show up to the first day of practice totally out of shape, and expect to be ready to compete 3-4 weeks later. Not to mention that many of today's youths lead relatively sedentary lives and are not just out of shape from a competitive standpoint, but also from a general population standpoint as well. Even if out of shape athletes do attend each practice, which is a big if, it is a challenge, not to mention a safety issue.
My method for GPP includes trying to discourage competition during workouts early on, and have athletes focus on a general progression of fitness and technique. I don't want to hold the athletes back that are ready for more intense training, but I also don't want those that are not ready, to over-extend themselves. A saving grace, however; is that young bodies are typically able to adapt pretty quickly, but knowing this shouldn't result in throwing caution to the wind, ie; have time trials for sprinters too early.
For my sprinters the initial focus is working on basic endurance, basic strength, and developing technique and race models through our warm up procedure and the early workouts. When any athletes run a distance that they perceive as a long way, and approach as an aerobic run (long distance), they should respect certain technique aspects to avoid over striding, and to minimize wear and tear on the body. Those not in very good shape will be in a survival mode for much of the training early on, and will just try to finish the training runs any way they can, but hopefully fairly soon will be able to run with some decent resemblance of good technique and strategy, and be able to, on runs they consider to be long, have a pace that feels fast but is not a strain and is not too difficult to hold.
I'm not a big believer in a lot of distance work for sprinters to build a base, but I do not totally leave it out as some sprint coaches do. Early on, rather than having athletes do a 20-30 minute run or a few miles, breaking it up in 600 - 800 meter repeats can be very helpful in producing a better quality of effort. Ladder workouts, ie; 600-500-400-300-200 can be used to build basic endurance as well as an introduction into an increase in intensity to help prepare for long sprints. When working with out of shape athletes, however; if you don't watch it, they'll be doing a lot of slow running when confronted with what they consider to be long distances. They may respond better with workouts with shorter distances and less recovery time, ie; some 300s with a 100 meter walk in between, and then eventually progress to something like two sets of 400-350-300, with a recovery walk of 100 meters less than the distance just run, and walking about a lap between sets.
Once again, running technique is important for safety and effectiveness. Sprint guru, Ralph Mann, describes what he calls "The comfort trap" when athletes try long sprints and respond to fatigue, trying to run relaxed by reaching out and jamming their touchdown leg in front of them and vaulting over the leg. This results in big impact forces, longer air times, very inefficient running, and again, unnecessary wear and tear on the body. A good initial goal is to try to prepare the kids to be able to put forth a respectable effort when running a 400 meter race.
At some point, when doing warm-up runs, you will notice that the sprinters will become more and more willing and able to progress to intense sprints. Marry this with workouts geared toward developing the 200 meter race model, ie; 150s. The most stressful part on the legs (hamstrings) is during the 90-120 meter zone where the athletes are to accelerate to top speed. Initially you may want to have them focus on a maintenance of speed in this zone and eventually a relaxed acceleration before encouraging a true max velocity acceleration. From there the focus can shift to the 100 meter race model.
I believe in conjugate periodization, so although there definitely is an effort to build a base, I like mixing up the different ingredients that go into building race fitness, ie; endurance, strength and power, speed, rhythm/tempo, cross training, etc... During GPP, however; the intensity of the work is relatively low, while we work at getting the volume up pretty high.
Prior to the first meet the athletes expected to run 400 meters in a meet will typically have worked their way up to being able to do some broken 400s in a decent manner. Those running the 200 should have done some intense 150s, and those running the 55 and 100 meter sprints should have done pretty much what the 200 meter athletes did, with enough attention given to starts, accelerating, and those race models.
It is critical to not pressure the athlete to run too fast too soon, and to not feel pressured to pack too many hard workouts into too short a time. Mixing in easy workouts, medium workouts, and days off at the right times is a crucial coaching skill, and requires re-evaluation and communication with the athletes. At the end of the day, if the athlete is not ready to sprint by the first meet, then he/she shouldn't sprint. Maybe run the 4 x 400 relay, field events, etc...