The next time you sit down at a poker table, you need to remember that every player sitting around that table has different tendencies. For instance, Paul might call your all-in when he's holding top pair, but Mary wouldn't dare think of doing so. Given the differences in player habits, it's imperative that you approach each player accordingly.
Here's the tricky part: You don't know what player tendencies are when you're sitting down to play. Fortunately, there is a way to solve this problem, but it requires a great deal of patience.
When you first sit down at a poker table, you need to play tight for at least the first hour. By doing so, you will be watching how the other players approach the game and picking up reads. For example, you might find out that Paul likes to raise to $15 pre-flop in a $1/$2 No Limit Game when he's holding A/10-suited or better. You might also find out that John will always limp-in with a medium pair, attempting to stealthily hit his set and win a big pot. And you might learn that James subconsciously taps his fingers on the table when he's on a draw.
Now imagine getting involved with these players when first sitting down, and without having all that information. You would be at a distinct disadvantage. Once you sit back and pick up all this information, it's time to go into attack mode, but don't get carried away. Patience and well-timed aggression are the keys to success.
Since you know that Paul will call your all-in when holding top pair, if you sense he has top pair on the flop and you're on a flush draw, then you're at a mathematical disadvantage. Therefore, you don't want to push all-in. Your best approach will be to bet half the pot, which can mean anything and keep Paul guessing. If he comes back at you, then you will have a difficult decision to make, but a lot will depend on how much money is already in the pot, and if you have him covered in regard to chip counts.
Let's say it's the same situation, but you're up against Mary instead of Paul. In this case, you want to push all-in when you sense she has top pair and you're on a flush draw. You want to do this because you know she will fold, and you will not have to worry about hitting your flush. Instead of gambling and hoping to hit the flush to win a big pot, you will win a small pot without any risk.
As you can see, the game of poker isn't black and white. You can't automatically decide to call, fold, raise, or push all-in based on the cards. Instead, you need to play the game by prying open your opponent's mind and figuring out what he or she likes and doesn't like to do. This will give you a significant advantage and should lead to increased profits.