From playing alot of poker MTT tournaments over the years I have noticed the same mistakes being made over and over again, even by seemingly winning players make fundamental mistakes when it comes to playing different size stacks. Its fundamental that you understand how both yours and your opponents stack size should effect how you play in poker tournaments, below is the guide:
10 BB and below: Every play you make should be an allin play. You are either open shoving your whole stack into the middle or your folding. Note that if your shoving over someones raise you need to be paying careful attention to your opponents stack size. If your opponents are good they will rarely be raise folding a stack size below 15 big blinds, so against a winning player you will often have n0 fold equity. If your playing against someone with a large stack they will often spite call you because its a small portion of there chips. The best people to shove over are people with a stack size that can raise fold often IE 15-25bb. Its also worth noting that the lower your stack the less fold equity you should have overall, someone shoving in 4bb from the button against a 15bb stack is going to get called alot wider than someone shoving 10 big blind from the button against a 15bb stack, this is because if the caller loses 10 blinds he is more or less crippled but if he loses 4 blinds he still has a playable stack.
10-15 BB: When there are antis in play it makes stacks shallower, because of this, its correct to be shoving allin preflop with upto a 15bb stack as your only play. If antis do not exist then you should only be raising if you have a hand strong enough to call an allin shove. If you dont, do not open raise, save your stack to give you more leverage when you shove allin or re-steal allin against someone. The only exception is if you are in late position and have a few super nits behind you who wont re-steal often at all.
15-22 BB: Is the smallest stack size where you can consider raise folding. You should generally be raise calling almost all the time with this stack size. There are times when you can raise fold, this tends to be against the tightest and least aggressive opponents who will not re-steal against you. For the most part you will be raise calling.
Starting at 15bb you start to get more fold equity on your allin raises so this is a great size to start re-stealing allin with semi bluff hands that have equity against your opponents raise calling range. You will want to look for spots where:
Your opponents raising range is wide and the likelihood they will fold to your shove is high. On top of this, if you have a tight image and a hand that has equity decent equity against there calling (suited connectors, suited broadway, pairs, suited aces) then it will be a good spot to re-steal allin as a semibluff and should be rather profitable. When called you will ususally have around 30%+ equity against there range. This will be a profitable play overall because your opponent will fold to your shove enough times to negate the equity disadvantage you have when called.
22-35 BB: With this stack size you have more room to maneuver and you can afford to be open raising more hands to try and steal the blinds and antis and accumulate a larger stack. Other players may be aware that when you have this kind of stack size you should be raise folding more so be ready to get re-stealed allin on by a wide range when playing against knowledgable short stacks. If your at a table with lots of players who will shove allin over your open raise you need to adjust by raising less hands overall and playing a tighter game.
Its also worth noting that re-stealing allin with this stack size can be a bit too large (Especially if you have players behind you with similar stack sizes to you). If for example you have a hand that is strong enough to want to get allin against another player in the 25-30bb range, I would 3-bet there original raise to 9-10 times the big blinds and shove all flops no matter what if they dont get it allin. The allin shove would be around pot size or slightly over pot and is completely acceptable.
35BB -45BB: The biggest mistake I see people making with this stack size is 3-betting preflop with the intention of folding to a 4bet. Anytime you put in 8-10 blinds with this stack size preflop and are folding to an allin raise it seems like its too much of your stack and to me, it seems like a costly error, especially if your opponent is 4-bet shoving with a wide range. If your playing against the type of oponent who will fold to 90% of 3-bets and will fold strong hands like TT and JJ preflop then this may be a profitable play, however, for the most part though I would not 3-bet fold this stack size.
Also with this stack size you can afford to be playing more hands overall. If it is early game I would still play pretty tight but if its at the anti stage there is still some good value in raising a wide range and taking down the blinds and antis.
Over 45 BB: This stack size allows you to have the most amount of maneuverability. You can 3-bet fold and also 4-bet shove over the 3-bets of your opponents (45BB actually is a great stack size to shove over a 9BB 3-bet with lots of fold equity), if you are in the middle or late game with this stack size, chances are you are one of the chipleaders in the tournament and will be able to leverage your stack size to the maximum. Congratulations, now go take it down!