When you ask how you can win when playing poker, you have clarify what that really means. Do you just want to win once in a while, have a big night, or do you want to consistently come out ahead over time? Too many players have the idea that they need to win a lot of hands, and so they lose money by not folding often enough. Others want to look good, and so are easily manipulated into staying with hands they shouldn't play.
I've watched a lot of good and bad poker players (I used to work in a casino). I also just recently did some research into basic strategies used by professional poker players. So if making money sounds better than winning many hands or impressing others, here is what I have found.
Play in the Right Game
Really smart players will tell you that your skill is not the most important thing. I know this from experience because I have never been a very good poker player, yet I have won far more than I have lost. What's my secret? I played against weaker players.
To win at poker, you have to drop the ego trips. This isn't a chess game or a tennis match, and you don't want good competition. You want the others to be clearly less skilled than you. If there are one or two players at the table who are definitely better, you'll probably lose more than you win.
Don't advertise your skill. Find games where the other players are relatively weaker, and let them think they are superior. Win as "quietly" as you can. Pointing out that you are always winning will just chase away the weak players who are responsible for your gains.
Playing the right game also means knowing what your comfort level is. If you can't play the same way at a high stakes table, you probably shouldn't be there. Choose a game where you can play your best game - a game where you won't hesitate over a bet you would normally make just because it seems like a lot of money. Instead of playing to win, you'll start to play to not lose if the stakes are too high for you.
Work your way up to higher stakes after you have some winnings to play with. You might also want to stay at the games where you win. You often can make more money at the lower-stakes games, because the weaker players are there. A good player can make some money at a $2/$4 game (In $2/$4 seven-card stud or Texas hold'em a player can bet or raise $2 in the first two rounds, and $4 after that). In $10/20 games and above, you start to get more professional players, so avoid these.
One thing all poker players should do, especially when starting out (and possibly forever), is to track their wins and losses. A simple legal pad will work for this. Just be sure to write down how much you lost or won every single time you play. Without this, many players convince themselves that they are better than they really are..
It is also good to make notes with each entry, specifying where you played, what other players were there, and personal conditions. The best players can have a losing night or week, but if you notice that those nights come more often when you have a beer or two, it could be useful information.
Watch yourself and be aware of where your strengths and weaknesses are. If you lose money during more than half of any ten sessions, you probably should reevaluate your play and/or find weaker players to play against. If you can't consistently read your opponents you probably need a different game and/or more practice at a low-stakes game.
If you find that you play noticeably differently when you are winning versus losing, you may not be ready to make money at poker. Accept that you will have losing sessions - just watch to see if they come too often. To be comfortable and play consistently, you should have a bankroll of about 20 times the maximum bet (some professionals say 15 times), and be ready to lose it. For a $5/$10 game, that means you should have at least $200 when you sit at the table.
Other Poker Tips
Know the odds. Do a bit of reading to learn how to calculate the winning chances for each given hand. Then learn how to calculate whether that translates into a good bet based on what is in the pot and what you'll have to bet. Numbers matter in poker.
In Texas hold'em bet good starting hands aggressively to chase players out. The fewer players that remain at the end, the more likely you are to have the winning hand. For example, the statistics say that a pair of aces will win against one other player 80% of the time, but if four players stay in through the first two rounds it will win only about 50% of the time. Strong bets on a decent pair effectively scares off hands that could have become winners.
Most professional players will tell you that you should fold early and often. On average you should be folding about 75% of your hands on the first betting round. Those who play almost every hand win more hands, but lose money in the end. To win more often, you should play a little tighter than the other players at the table.
On the other hand, don't play too predictably. An occasional bluff might win a hand. If it doesn't, you at least have made your play less predictable. Wild play and bluffing are not actually a big part of how to win when you play poker (especially limit poker), but they have their place.