It is pretty much commonly accepted by most Tetris 'circles' that the practical way to make a Tetris is to leave a gap on one side for the straight tetrad to slide into, if and when it appears. But, which side should be reserved for this task?
Several of you keen observers noted that the tetrads enter the screen a little to the left of the center. This means that straight pieces can go to the far left side quicker than the right, which can be especially critical at the higher levels. Thus, it would probably be advantageous to leave your Tetris gap open on the left side, not the right. Those of you who are used to the Westernized convention of progressing from upper-left to lower-right will have to reverse polarities.
Here's a simple memory aid through multiple associations:
Tetris = Soviet Union = Communism = extreme left wing.