One of the most frequent mistakes I see during tournaments are players not understanding their, or their opponents’ stack sizes in relation to the blinds and antes. The most common error players make is trying to calling with too many speculative/drawing hands (for example suited connectors, weak suited Aces, K10, Q9 etc) when they just don’t have enough breathing room in their stack to be speculating with! Whilst those hands can be fantastic to win big pots with when deep-stacked 70 big blinds or more, they cost too large a % of a short stack to try and make big hands (i.e. straights and flushes), particularly when facing aggressive opponents.

So what do I mean by a short stack? For simplicity, let’s say 35 big blinds or less is your cut-off for calling raises with these types of hands (in or out of position). Do note however that these hands are still good to be selectively AGGRESSIVE with on a mid-short stack.
In a tournament you can’t wait around forever for premium hands, particularly when shortstacked so marginal hands like this are good for picking up small pots pre-flop or on the flop.
Also remember that it’s not just your stack that you need to be aware of! Look for people who have awkward stack sizes to apply pressure to… for example, 3betting an active player who is opening a lot on a stack of 25bbs can be very profitable as they will need a real hand to 4bet shove… as it looks like they have no fold equity and so can’t easily bluff back at you!