I had about six months to train for the marathon. I'd been running 3-4 miles a few times a week for a few years. So, I thought I'd run 5 miles a day for a week, then 6 miles a day for a week, and add a mile every day each week and run that distance every day til I got to 15 or 20 miles per day.
I believe it was someone on CB that set me straight and showed me how stupid I was, luckily, before I got too far into it. It was then a Hal Higdon training plan that got me through the marathon.