Take regular breaks when playing poker. Avoid playing long sessions

As you play, one of the single best things you can do is observe your opponents, even when you’re not in a hand. If you know that one player always raises in a certain position and another has a poker tell when he bluffs and a 3rd folds to every re-raise, you can use that information to help you decide how to play against them. Once you know that player 3 always folds to a re-raise on a river, that’s when you can bluff and steal a pot.