Mr.Thunders
Striker
Try some interval training. Running hard for a defined period with rest in between; eg. 4x5minute runs with 90 secs rest between each or 10x2mins with 75 secs rest. If you train on a track sub the time for distance, eg. 4x1mile or 16 x 400m.
Pyramids is good one too . . 1min, 2min, 3min, 4min, 5min, 4min, 3min, 2min, 1min.
Try to find a route that's fairly flat so you don't end up doing one effort up a hill. I train on an industrial estate normally.
Try to do two sessions a week doing this sort of stuff, mixing up the distances a bit. . . you'll feel the benefit.
There's a fair bit on the net about this, search interval training or fartlek.
good luck
Do you run flat out for these periods? Doing 7 m/m at park runs,tempo pace for my half marathon training is 7:24