I always found pyramid sessions worked for me. 200, 300, 400, 500, 800, 1000 and back down again with 100m recovery after each rep (200m as a special treat after the 1000m!)
Certainly worth a go if you can get to the track, alternatively, if you have access to a treadmill rather than a track, then try it on a timed basis eg:
4 min warm-up
2min at 12kph @ 1% incline
1min at 9kph @ 4% incline
2min at 13kph @ 1% incline
1 min at 9kph @ 5% incline etc... then back down again.
Obviously pace is according to how fast you are, but the higher incline recoveries are good!
