Run a lap within 1 min 15 s, then rest for 2 minutes (3 if you
can't run the next lap within that time, you can shorten it in the
future). Do this 6 times.
When you get used to it, shorten the rest period, or try running
2 laps within 2:30 (thrice), or 3 within 3:40 (twice).
Don't underestimate the importance of recovery between
trainings.