Improving your running mechanics and strength will help, but you should also include interval work with your longer runs to train your body's energy systems for speed. Twice a week, perform sprint intervals (400 meters and 600 meters) or hill climbs and keep your distance up around 15-20 miles for the rest of the week.
400-meter sprint intervalsHow to do it: You'll start by sprinting 400 meters for six repetitions, resting one minute between sprints. Start running slowly in your first rep and increase speed on each one so the last rep is your fastest. Keeping an even pace on all reps is OK as long as the last one is still faster than the rest.
600-meter sprint intervalsHow to do it: Same basic idea as the 400-meter sprint intervals, but aim for six to eight repetitions, or sprints, and increase your rest time between sprints to two minutes. More advanced runners can try decreasing the rest time to one minute or work up to 800 or 1000 meters with two-three minutes of rest between reps.
Hill runningRunning hills can also help improve speed and power. How to do it: Find a hill that would take you three-five minutes to climb. Jog up the first three-quarters of the hill and then sprint the last quarter. Jog back down and repeat three-five times. Your goal is to get to the same spot on the hill during each sprint. You can also do the same thing on a treadmill, so you'll run for three minutes and then sprint for the last minute, nudging up the incline each minute.
Here's a nine-week progression that makes use of these techniques and incorporates your distance running:
Week 1- 6 x 400m
Week 2- 8 x 400m
Week 3- Hills
Week 4- Distance jog
Week 5- 6 x 600m
Week 6- 7 x 600m
Week 8- Hills
Week 9- Distance jog
-- Paul Robbins, Metabolic Specialist, Athletes' Performance