As the other guide has mentioned, the trick is to keep the screen as empty as possible on the final level, don't be tempted to try go for 'Tetris' clears or combos, just keep the stack as low as possible. The only thing I would add is that even if at the start you are comfortable and managing the game well, don't be tempted to press 'up' on the D-Pad to do the instant drop. Keep your eye on the top right on the next upcoming shape, then you are constantly one move ahead and keep on top of things. Sounds obvious, but when I mentioned it to my girlfriend she didn't realize it was there! Finally, DO NOT GIVE UP. My final 5/6 clears I was about 2 lines from the top. Even if you think you're losing control, you can still get 1 or 2 clears here and there and it all adds up.