I have now been running for over two years and have tried a number of methods to increase my speed and endurance for the long run. I've tried speed work, longer recovery periods, hill training, and yes and combination of them all. I am currently in the process of preparing for my first Marathon in October. I've looked over a variety of programs to include: Hal Higdon's Marathon Training Guide and programs offered by running clubs, magazines and others. I've tried to glean the best of the programs to get to where I think I need to be by race time. Here is my program which is based on a series of build ups and breakdowns with a long hill run every week.
I generally run 6 days a week, at distances between 5-7 miles. I end the week with a long hill run. The key here is the long hill run. On a build up week, I start off on Monday or Tuesday building up my pace over the week to get to the long run over the weekend. Build ups occur over a three week period, so by the end of the third week, I've increased my long run by over 1 to 2 miles. This means that during that build up period, my long run increases a 1/2 mile each weekend for three consecutive weeks. I started at 10miles and am now up to around 14miles after two months of training. Every three weeks, I reduce my long run down to 10 miles to break myself down and then start to rebuild at longer distances. The long hill run has not only built up my endurance, but has increased my pace. I have tested this theory during a few 10 miler events and have found that I have set a new PR each time. So try the hill!