When you have a full stack, the top enemy can be taken away. Let us say it is a Goomba at the very top of the stack, move that stack underneath a queued Goomba, and voila, it will disapear.
Try clearing the Eggs rather than building for higher scoring opportunities. You will get your higher scores naturally, so just let them come naturally rather than trying to force a bigger Yoshi to happen.
Look at what is in the queue before you rush the current falling pieces to the ground. This allows you to shift some of the stacks ahead of time, which will allow you an easier time with the next placement.
In Type B, always eliminate a pair even if it means sacrifcing an Egg Bottom pair.
Always try keeping one step ahead of the game. Move Mario to a position where he will be able to make the next move quicker. and to do his moves more efficiently.
As the game speed increases, try keeping your stacks lower.
Always try keeping as diverse of an enemy pool available for matching up as possible. This allows you to not have your excess monster piles get too large.
If you absolutely must stack some double types of enemies, always check the Enemy Queue first. This will allow you to plan ahead of time so you can minimize the pile up being started by the excess monster piling.
Start out on a slower speed so you can get the hang of the game, and then go up to higher speeds when you need a greater challenge.
You will notice that the Egg Tops and Egg Bottoms come in streaks. This means that you as the player should recognize the start of a dry spot for these eggs, and keep the egg stacks clean accordingly. If you fail to recognize this pattern, you will quickly find your stacks becoming unmanagable.
You can eliminate two enemies from one stack in a single pair. Eliminate the top matching enemy (say it is a Boo), and then swing the stack around to get the second enemy before it falls past the now lower stack (say it is a Pirahna Plant). This is an excellent way to avoid having unwanted enemies stack up on other enemies.