Five of the seven cards eventually dealt are viewable when you see the flop, that's over 70% of the available information. At this point you should have a good idea of how strong your final hand could be.
Don't go chasing cards, fold if necessary! Sometimes you should limit your losses if your hand isn't great and decide to fold early in the hand.
Don't try to play every hand. The most popular mistake for beginner players is playing too many hands. If you play any two cards with the hopes of hitting a great flop, you will often make the second best hand. This will result in your chips wasting away as you pay for missed flop after missed flop.
Don't solely focus on your hand, take into account the actions of other players and what type of hands that their actions suggest that they may have. This may lead you to fold a strong hand if you feel that, with the community cards available and the betting behavior, a player may have an even better hand.
This may sound a little complicated but once you're thinking about what your opponent has, you should try thinking about what your opponent may think that you have. It's simply a case of putting yourself in your opponent's shoes and trying to think what your actions may be telling him. This behavior is key in the art of bluffing.
It's important to find a game with a stakes level that you feel comfortable at. You should be playing at stakes that are not so high that you are afraid to make the moves you need to make, but not so low that you play carelessly. If you're not sure, err on the side of caution and play lower stakes. You can always progress to higher stakes if you're sure that you're not being challenged enough.
Always analyse your play. Look back at important hands and consider what you did right and what you did wrong, and how it impacted upon your results. If you identify a real error in your play, you can then try to correct it before your next game.