In poker it is important to understand how your opponents think. There are a few player styles that are good to keep in mind:
Tight - Loose
A tight player plays few hands, waiting for cards like pocket pairs. The loose player sees opportunities instead of obstacles. Thus he is guaranteed to always be in on the action.
Passive - Aggressive
A passive player is always careful and difficult to trap. Such a player both wins less and looses less. An aggressive player acts the other way around. If he got a good hand, he will go for it. This makes it easier to bluff but more risky.
Pro - Casual
The pro player tries to play thinking like a pro, but risking to tilt when a streak of bad cards hits. The casual player has a more relaxed attitude and is guaranteed to have much more fun.
Einstein - Chameleon
Einstein plays by the odds and does not really bother about short-term winnings or losses. The chameleon player adjusts tactics due to the other player's tactics.
GENERAL STRATEGIES
Selecting the right game
There is a huge difference in how to play fixed limit, no limit and pot limit poker. Find the game that suits you. Remember that the higher the stakes the better the players are!
Study your opponents
Think about your opponents style and try to get inside their heads.
Not being to curious
Curiosity will certainly make you loose a lot of money in the long run ("What if!?"). Because any two cards can win, it is always tempting to stay in the pot!
Know when to fold
This is something you will have to learn. Soon you will know the feeling "I KNEW he had a a pair of Kings and I KNEW he got that triplet!". So why did you stay in??
Biggest loser
The biggest loser is always the one with the second best hand.
Resist Tilting
Tilt is when you go emotional and bet on cards you would not normally bet on. This normally occours when you loose against all odds or when you get super-lousy cards for a long while.
Pot odds
Think about how much money is in the pot before you decide if you are going to bet or fold.
On bluffing
Remember it is much harder to bluff a poor player than a good one!