Incorporate an off-season into your long distance running schedule. Take one to three months off each year and use other aerobic activities to keep your body in good cardiovascular shape. This change will keep your mind sharp and your body from injury.
Remember to stretch and strengthen sport specific muscles for long distance runs. Keeping your hamstrings and quadriceps strong and lengthened will help improve your stride, your ability to run distance and decrease the soreness you may feel after a long run.
And the last, and fun, running tip for long distance runners is to use massage over their lower extremities after a run to decrease the amount of lactic acid build up in the muscles. Lactic acid is a by-product of metabolism. Quite a bit of lactic acid is built up over long distance runs and it is deposited in the muscle until the blood can clear it. By massaging the muscles and staying hydrated you can help to release the lactic acid and therefore decrease the muscle stiffness and soreness after a long run.