Poker is a card game of chance, but when betting comes into play it becomes much more a game of skill and psychology. Learning the basics of poker can be as simple as memorizing a few charts that indicate what beats what (a flush beats a straight, three of a kind beats two pair, etc).
The best way to improve your skills at poker is to practice constantly. You can do this by playing in tournaments, at home games with friends, or even in online poker rooms. It is also recommended to read books on the subject and take notes while you are playing. This will help you to develop your own strategy, which can be tweaked as needed.
When playing poker it is important to be in a good mood and not to let frustration, fatigue or anger get the best of you. Poker is a very mental intensive game, and you will perform your best when you are happy.
It is also a good idea to avoid calling out your opponents for mistakes they make. While their mistake might bruise your ego, it is better to let them learn their lesson and move on. After all, they are going to make mistakes in the future, and the more they learn, the better they will become.