My first big mistake I think is the most common one. When I started playing Hold'em I was trying to play cards. When you play cards, you are trying to have the best hand. This is a terrible way to play Hold'em. There is too much variance in the deals for one to have the best hand often enough. If I will ever be known for a poker quote it would be, "Poker is not a card game. It's a betting game with cards." As soon as I realized that it was the betting that was more important than the cards, I started to become an actual player. Until then, I was just some clueless putz handing away chips while trying to build the best hand. The cards are random. You have no control over them. But you have complete control over your action/betting. Furthermore, most pots are won without showdown, so you don't always have to have the best hand.