While building an endurance base is the most important aspect for beginning runners, it is clear that you don't just increase your mileage forever. No one can maintain peak shape , train at maximal levels and race all year round. Elite and professional runners plan very carefully for their racing seasons. They begin by first building base, then adding specific sharpening or speedwork, allowing some rest by tapering, racing and finally a period of resting and rebuilding. This comprises a single season.
Many runners do two racing seasons a year.
The miles should first be added to the extra long day, then to the midweek longer runs and finally to the easy day. The base building period may be from 2 - 6 months depending on the starting place and the final goals. After the racing period, there should be a period of reduced training, rest and recovery leading to another sequence of base and strength building. The rest periods are for both physical and psychological recovery. Because of the physiological requirements for distance running, it is possible to train endurance and speed separately.