For an easier game press and hold up and start while on the title screen.
Every time you move a piece over, the game counts it. The more you move it, the game thinks you have more trouble with that certain piece, and will dish out more of them. You can exploit this every time you get a Tetris (Long "I" shape) piece, just move it from side to side as it falls. You will get it more often every time that you do so.
If you're playing Tetris 2 on the Super Game Boy, pause the game and press the A button to change default border to a new hidden one. Keep pressing the A button to select from 5 different hidden borders.*This only works on the re-release version of Tetris 2 with SGB support