This is a nice practice routine that I picked up from Dartsnutz.net. The idea is quite simple and allows you to have a short intense 20's practice session. The idea is that you throw 100 darts at the Triple 20 and track what you hit. As you can see:
At the pub the other day I wrote 1 thru 33 (and added the +1 to represent the lat 1/3 round) so that I could track the game easily, and notated the hits each round. A '1' represents a single 20, a '3' represents a triple, etc. So a notation of '113' means I hit 2 singles and a triple.
in the game above I use the Voks Bandits. One pleasing note regarding that game is that I didn't have any dead rounds until that last third round. I only had one dart and it missed wide into the 5, as I recall.
I've only played this a couple times, but score 78, which I am hoping is not bad but can still be improved upon.