Non-overstacking Construction
Overstacking can be very dangerous against an agressive opponent. If a player is not able to get down to the garbage efficiently, he'll be overwhelmed by garbage.
In this situation, a player overstacks and takes longer to get down to the garbage.
With the same sequence of pieces, a player can opt to switch the position of the T and the J, resulting in a clean opening for the garbage.
Towering
When facing an ever changing system of garbage, often, a player has to make the field uneven in height to avoid overstacking.
Be wary when towering because it's not always productive. If a player is not careful, he may end up severely decreasing his options in tetromino placement.
Field Manipulation
Garbage
Mis-drop
Skimming
Downward
When a player is starved of I tetrominoes and garbage is coming at a fast rate, he has to learn to depend on other tetrominoes to keep him from topping out.
Upward
Field Flattening/Fixing
Pyramid
Situations like this should be remedied as quickly as possible in a match to avoid future complications.
Overhang
When plagued by an unfortunate sequence of next pieces, an overhang is another form of a scapegoat.
Alternative Line Clear
Back-to-Back Chaining
Tetris
T-Spin Single
T-Spin Singles are the easiest to spot and to exploit in multiplayer. Not utilizing them will only put you at a disadvantage against an opponent who does.
If a situation is not readily available, create one if you don't already have a BtB chain going.
T-Spin Double
Timing
Offensive
Defensive