Warm up carefully, for at least 20 minutes. Set your stopwatch and prepare to run 2000m. If you manage to run 2000m under 7:30, switch (next time) to 3000m. Ideally, you should run on a 400m track, but a flat road will also do as long as you can somehow measure and mark 2000 (or 3000) metres. Try to run evenly and start the first few laps at 90% of what you consider your maximum speed and only push to 100% on the last lap.