Soccer is a sport that requires walking, jogging and running for long periods of time in a 90-minute game. The off-season is the best time build up the kind of endurance needed for weekly soccer games. Here is a three step process to improving endurance leading up to the season:
The fastest way to increase endurance is with interval training. The method here is to do short bursts of all-out effort followed by a short rest period. This should be repeated for a minimum of four minutes. This protocol should be followed only once a week at most.
Building endurance will also take some time on the track of the treadmill. Daily runs will go a long way to building a good base that can be improved by techniques like interval training. The basic math here is that if you ran a mile for five days a week, you could run five miles in a single session. The increase in miles needs to be done slowly to avoid any injury. The recommendation is not to increase distance by more than 10% daily.
The long run is a single weekly or monthly run that is several times longer than your daily runs. A two mile daily run should result in a long run distance of about ten miles. It is probably a good idea to not run the day before and the day after the long run.