Some players don't even realize that a play they are making is a mistake or a leak. In order to help you gain a better understanding, here are some examples of the biggest leaks you will typically see tournament poker players have and a brief explanation of what you can do to correct them.
#1 – Playing hands out of position – without question this is the biggest mistake, leak, blunder, whatever you want to call it that people make. This has been said in numerous places but it's always worth repeating. With position you get information. With this information you obtain power. Position is power. When you play hands out of position, you put yourself in situations where you will be reacting to the bets and raises of others rather than applying the pressure yourself.
Start folding hands that you think have value in early position but realistically do not. This includes hands like A-J (and even A-Q at certain tables), K-Q, suited aces, and suited connectors. Play these hands when you are in later position and have more knowledge about what is going on in the hand. This does not mean that you always fold these hands. In certain situations, like when you haven't played a hand in two orbits and have established a tight image, these hands can be playable from early position. However, over the long run, all you'll usually end up doing is donating chips to your opponents.
#2 – Betting improperly – this goes two ways. Some players bet too little and give their opponents too good of a price to continue in the hand. Other players bet too much and either lose too many chips in marginal situations or lose value for their strong hands because of the amount they bet. The goal when making a bet is to either induce your opponent to fold when you don't want a call or to induce a call when you feel that you have the best hand.
The art in betting is figuring out what the threshold amounts are for the opponent you are up against. For example, if you are bluffing, what amount will your opponent typically call with the hand range that you think they have? What amount will they fold to?
You want to make your bet the smallest amount possible that will still have a high probability of success. For some players, this amount could be as small as a minimum bet. With others, it could be pot sized or more. Then there are those who won't fold regardless of the amount you bet.
Figure out through observation of your opponents what their threshold levels are and make the appropriate bet. However, don't make the mistake of only betting a certain amount when you are bluffing and a different amount when you have a legitimate hand. The bets for those two types of situations need to be similar.
#3 – Not understanding the current tournament situation – if you watch enough poker, live or on television, you will see supposedly very good poker players fail to understand where they are at in a tournament. For example, one hand at the World Series of Poker, Phil Hellmuth blinded himself down until he was forced all in from the big blind. Did he move up 100 spots in the pay scale? Sure. In doing so, however, he essentially removed any chance at all at winning the tournament. It was also not uncommon at the WSOP to see players moving all in pre-flop for 50 big blinds. Or going all in with just top pair with 100 big blinds behind them. This wasn't just the occasional mistake either, it was happening time and time again.
It is extremely important that you know how your stack size shapes up in relation to only one thing. The blinds. Too often, what happens is a player sees that the average chip stack is four times the size of theirs and they panic and think they have to double up immediately without realizing that with 40 big blinds in front of them, they have plenty of time to wait and pick the correct spot. On the same token, many players pull a Hellmuth and fold hand after hand and give themselves basically no shot at winning, and in many cases, no shot at cashing because they tighten up too early. If you're getting short, take the calculated risks you need to get back in the game. If you are still deep relative to the blinds, then don't panic.
The Main Holdem Strategy Index: The Great Game of Holdem