How To Get Better At Chess

1. Watch better players play, and study games from better players. There are many great games by World Champions and Grandmasters at places like Chessgames.com. It would be best to play through games that are explained (annotated) at a level you can understand, otherwise you won't know why they made the moves they did.
2. Try to play stronger players. Ask them for advice after the game on what mistakes you made and how to improve. However, remember that their advice may not be correct!
3. Learn a specific opening such as the Ruy Lopez. Play through master games that use the same opening at Chessgames.com. Study books that are at your level on it. Keep using the opening for months or years until you are comfortable with it. Most players only need to know 1 or 2 openings for white and black each. Use opening databases at Shredder and ChessOK to find out popular opening moves.