First of all, do a good warm up. Probably at least 800 meters, or over 10 minutes. The main set is all 50s, and it works best with an old-school pace clock. You leave on the top (when one of seconds hands hits the 60), and swim a 50. The next 50 you leave on 1 second after the top, swim a 50... then next you leave on 2 seconds after the top and swim a 50, then 3 seconds after, etc. You keep doing this, but the catch is that you have to come in on the top every time, and as soon as you come in past the 60 you're out. Of course you can do it with a digital pace clock, but the analog one is more fun; the suspense builds as the arm sweeps around to the top.
|Old-school pace clock. Pick one colour of the seconds hands,|
and you have to get in after each 50 before it hits the top!
You end up getting less and less rest after each 50, so the key is to see how many 50s you can get in before you're out. One tip - don't sprint the first few as you have lots of time early on. You're going to need to sprint - hard - later to make the time cut off, so don't burn yourself out.
It's a great speed test to see if every time you do this, you can get at least one more 50 in compared to your last time.
Have fun, and let me know how many 50s you got in!