Knowing when you're beat
Most people love to talk about huge pots they won, rather then huge pots they folded in. Who can blame them? They just won a huge pot and want to share it with the world. However, winning a large pot is just as important as saving you from losing a big pot. Although you won't see great folds plastered around the internet, they are still vital towards making money in poker.
The trouble with a lot of players is they wish to be a "pro" player. So much that they want to make that great call or read on a player, even when they are pretty sure they are beat. They end up trying to make a great call and the pot gets shipped to their opponent. This can severely damage your bankroll until you get over the fact that to win at poker, you just need to make simple plays and moves, not hero ones.
Most players get drawn into big hands and almost get pressured into playing badly due to the size of the pot. Every single poker player has convinced themselves to call a big bet because they have talked themselves into believing they have the best hand or their opponent is bluffing etc. You have to get over this yourself, simply by taking a moment to think about what you are doing before instantly clicking the call button. Think about how the hand has been played out by your opponent. Then think about whether they would actually be betting that much into a pot with whatever hand you are putting them on. After considering this, analyse how you yourself played out the hand, whether you showed strength or weakness on each street and decide if this may have contributed to how they have sized their bet.
Beginner players think their opponents are bluffing a lot of the time, which is simply not true. They may have watched too much television poker, in which they show the best hands which often includes the best bluffs. This paints a picture of poker which is misconceived by a beginner. Players do not bluff every other hand, nor do you get aces or kings dealt every hand as is also shown on television poker.
Knowing when your beat is not really a skill, it is more an observation. You already have the skills to know when your beat, you just have to use them. Take your time and simply analyse how the hand was played out, and whether they would actually be betting with a worse hand then the one which you are holding.