The biggest mistake for beginner players is playing too many hands and playing too passively. It is important to wait for decent hands and throw away the junk hands. The big pairs such as AA, KK and QQ are by far the most profitable starting hands in poker. It's very important to play them in a way that maximizes your profit because these hands have a very high positive expectation and are rare. Just like other situations in poker where you have the best of it, you want to build up the pot quickly.
In most situations, when you have a big hand you want to build up the pot by taking the lead with betting and raising. However, there are some situations where you may want your opponent to be the aggressor and do the betting for you. You do this when your opponent is super aggressive and they bet and raise frequently with poor holdings. You should play it a bit different if you have a large stack nearing 100bb or more. This is because if you get it all-in on the river with a big stack, you will almost always be beaten by a two-pair hand or better. As the stack and pots get bigger, the better the hand you need to see a showdown. Often even strong hands like two-pairs and sets are no good when a lot of money goes in the pot on later streets. So if someone re-raises you on the turn or river with scary community cards, you may want to think about folding your high pair.
When you play a hand in poker it is important to plan the hand in advance. Why are you playing that hand and how are you going to play it? Too many players just play the hand because they like the look of it. They have succumbed to the "calling reflex" which is the idea that people have a tendency to want to call, even often without thinking about it beforehand. People don't come down to the local casino or play online to just sit there and fold all day. Small pairs and suited connected cards can be very profitable in no-limit hold 'em. Hitting sets and making flushes and straights have the potential to win big pots. They are often quite deceptive, especially straights like double gut shots, which are very hard to see and put people on sometimes.
In most situations, when you have a big hand you want to build up the pot by taking the lead with betting and raising. However, there are some situations where you may want your opponent to be the aggressor and do the betting for you. You do this when your opponent is super aggressive and they bet and raise frequently with poor holdings. You should play it a bit different if you have a large stack nearing 100bb or more. This is because if you get it all-in on the river with a big stack, you will almost always be beaten by a two-pair hand or better. As the stack and pots get bigger, the better the hand you need to see a showdown. Often even strong hands like two-pairs and sets are no good when a lot of money goes in the pot on later streets. So if someone re-raises you on the turn or river with scary community cards, you may want to think about folding your high pair.
When you play a hand in poker it is important to plan the hand in advance. Why are you playing that hand and how are you going to play it? Too many players just play the hand because they like the look of it. They have succumbed to the "calling reflex" which is the idea that people have a tendency to want to call, even often without thinking about it beforehand. People don't come down to the local casino or play online to just sit there and fold all day. Small pairs and suited connected cards can be very profitable in no-limit hold 'em. Hitting sets and making flushes and straights have the potential to win big pots. They are often quite deceptive, especially straights like double gut shots, which are very hard to see and put people on sometimes.