To increase your average running pace, you have to train your body to run faster. You don't have to run the entire distance at the same speed, but adapt your speeds so your average increases. You can get an average pace of eight minutes a mile, for instance, by running the first mile in 7 1/2 minutes, the second one in 8 1/2 and the last one in eight minutes.
Use a "hard/easy" principle, combining periods of running faster than your normal pace with regular workouts. Use interval, fartlek and tempo runs for speed sessions and keep your normal training runs at the same pace, but gradually increase the pace of these as your speed work takes effect. Train at your normal nine-minute pace, for instance, until your body adapts to the speed and you can slowly increase the normal training time.
Build a solid base of running, preferably at least 20 miles a week, before you start speed work, which will add strain on muscles and tissues. Limit speed work to one or two sessions a week of sprint or other drills. Use a track or a path with measured distances so you can judge intervals. Start with a base of your current pace; for instance, 31 minutes for 5 kilometers is a 10-minute mile. Set a goal for how much you want to improve that pace.
Intervals are short, intense bursts of speed, with rest between. Do repeats, running the same distance repeatedly with rest between; pyramids, shorter sprints working to longer ones, then back to shorter, or ladders, gradually increasing the distance of each sprint. Use a measured space and intervals like 220 yards or 200 meters. Vary interval speed; run each interval a bit faster, then taper back down to your starting speed. Rest between each interval.
Incorporate fartlek training in regular runs. This is a Swedish phrase meaning "speed play." It consists of interjecting bursts of short, fast runs into a daily routine, but unstructured, without a fixed speed or distance. Run fast for 30 seconds or between two lamp posts, for instance. You can vary a fartlek run from 15 seconds to three minutes to train your body to run faster. Start with short fartleks and gradually increase the length as you build speed and endurance.
Tempo runs (advisor) are runs at a pace faster than your normal workout, but for a shorter distance. (connect) You should run at 80 to 90 percent of your usual pace for a third to a fourth of your usual distance, or your usual time if you run by time. Maintain that pace consistently for the full distance or time. Tempo runs build speed but teach pace, to maintain a uniform speed.(ref: running advisor, running bug, runners connect, running times).
Hill repeats build strength which will translate into more speed and endurance. Run up a hill at your normal training pace, then jog or walk back down and repeat the performance. Concentrate on lifting your knees and pushing off hard on every step.(ref: running advisor, cool running)