find a track, and do repeat 400’s, 6 of them, at about 10–15 seconds plus your best (so if you can currently run 60 seconds, do 6 at 70, but if your best is 80, drop it down to 95).
if you’re not really into timing yourself, just do them at “90%”
remember to warm up and stretch first, and do cooldown afterward.
another great workout is split 800’s (usually three of them)
500, then 30 second rest, then 300, then a full rest (2–3 minutes, do a slow jog to keep your body warm and not cramp up)
then 600, then 30 second rest, then 200, then full rest
500, then 30 second rest, then 300, then a full rest
for endurance, find a good bit of woods or fields that has trails on it, and go out for a long run (30 min – an hour, or 4–10 miles)
the best thing to do is just make sure you run at least 4 times a week.