My particular running schedule comes from various plans that I read in "Runner's World," taking advice from more experienced runners, plus my own trial and error. If something seemed interesting, then I would try it and see how it worked. If I liked it, then I added it to my program. If it didn't work for me, then I didn't do it again. I've found that running 4 days a week works best for me. I have one long run, one short (5 km) run, and two medium length runs every week. One of the medium runs includes hills and the other is in the valley, where it's flat. These days I've been alternating my long runs in the hills and on a flat route. I don't follow a set plan, other than the weekly long run. This flexibility works for me, because I have a lot of self-discipline and am internally motivated. I'm able to easily change my running schedule based on any changes in my work schedule. My training plan may not work for someone who is just starting out running or who lacks self-discipline.
When I want to run a marathon or half-marathon, I get out the calendar and plan out my long runs. I tend to plan more long runs than most training programs use, which often puts me ahead of "where I should be" at a given point in time. There are a couple of reasons for this: 1) The only way to prepare the body for the marathon or half-marathon experience is to do long runs. If I do enough long runs in training, and gain more experience by doing them, I'm better prepared for anything that might happen in a race. I'm also more confident in my ability to go the distance. 2) If I get sick, injured, feel like my body needs a little break, or go for a hike or bike ride instead of a run, I know I will still get in enough long runs to be fully prepared for the race. I can skip a long run now and then without feeling guilty.
I never understood the training programs which take a person from "Zero to Marathon in 12 Weeks." Some people swear by them; and runners using them have finished marathons. But they're not for me. First of all, they build up the mileage too quickly for my knees. It takes me longer than a lot of people to train for a long race because of tendinitis in my knees. If I build up gradually, I don't have any problems. The other problem is that they only have one (or two maximum) runs in the 18-20 mile (30-32 km) range. As I said in the preceding paragraph, that's not enough to really prepare the body for a marathon.
When I had a blog on Yahoo 360, there was a woman who followed a 16 week marathon training program to the letter. It seemed like she just couldn't deviate from the plan no matter what was occurring in her life. She ran strictly for mileage and would have her husband drive a course to get the mileage exact. I read her blog on 360, mainly because I was fascinated that someone could be so rigid in following a program. This woman did every single workout exactly as it was written in the plan. To her credit, she finished the marathon, so following that program worked for her. But her way just wouldn't work for me.
The thing about running is that it just doesn't matter how long or far you run, or if you strictly adhere to a particular plan or have more flexible workouts. What matters is that the program that you choose to follow works for you.