Every chess game begins with an opening, which means that when reviewing your own games, it's important to analyze what happened in the first few moves. Here are three ways to improve your openings:
1) Evaluate the outcome of the opening. Did you get a good position? If you were able to get control over the center, develop your pieces to good squares, and castle by around move 10-12, you're in good shape. If not, make sure to analyze the game with a friend, a coach, or an engine to see where you could improve your play.
2) Expand your knowledge of opening theory. Whenever you face a new opening or a variation that you haven't seen before, research the existing theory of the line so that you're better prepared the next time someone plays it against you. Over time, you can build up your opening knowledge and be ready for anything in the first phase of the game.
3) Study master games in the openings that you play. Learning the Najdorf Sicilian? Look up the games of Bobby Fischer to see how he handled this classic opening. By studying games of strong players, you can increase your understanding of the opening and have a good sense of the various plans possible in the eventual middlegame.
So let us know how this tips have helped you in reviewing your openings.