Posted this before but since its marathon season again:
3 week marathon cycle: repeat 2 to 4 times followed by a 2 week taper.
Day 1: Recovery Run
Day 2: Easy Distance Run
Day 3: Easy Distance Run
Day 4: 10k run @ 95% of marathon race pace
Day 5: Easy Distance Run
Day 6: Easy Distance Run
Day 7: 24-26 miles @ easy pace
Day 8: Recovery Run
Day 9: Easy Distance Run
Day 10: Easy Distance Run
Day 11: 10 miles @ marathon race pace
Day 12: Easy Distance Run
Day 13: Easy Distance Run
Day 14: 20-22 miles @ 107.5% of marathon race pace
Day 15: Recovery Run
Day 16: Easy Distance Run
Day 17: Easy Distance Run
Day 18: 6 x 1600 w 400j @ 90% of marathon race pace
Day 19: Easy Distance Run
Day 20: Easy Distance Run
Day 21: 14-16 miles @ marathon race pace
fill in recovery days, easy distance days, warm-up, cool-downs and any secondary runs with whatever mileage necessary to achieve your desired mileage target.