Basic Opening Principles
There are potentially three parts of a chess game, the opening, the middlegame, and the endgame. The opening tends to cover the period of the game while you and your opponent begin to get your pieces into the game, perhaps the first 10 to 15 moves. The middlegame is the part of the game after the opening and before the endgame. The endgame is everything after the middlegame. You know what those two parts of the game are simply based off their prefix.
Opening principles are a blend of chess strategy and potentially tactics that applies early on in a chess game.
1. Don't give away material.
Note what your opponent is attacking. You'll probably find this as the only opening guide in existence that starts off with this, but it's super true. Example below of when you fail to do this.
Your opponent may legitimately make a mistake early on in the game. When your opponent gives you material, take it unless you see an obvious repercussion such as a recapture or tactical trick. Example below.
Some beginner's freak out about central control. It's not really necessary. Just it can be bothersome when you completely disregard the center and your pieces can often be harassed easily and it's harder to develop your pieces.
4. Develop your pieces
Getting them off the back rank and into the game is how you develop your pieces. Make sure you put them on safe squares.
5. King Safety
This is related to development. You want to castle early on so that your king is not in the center. (I suggest on kingside as it's slightly safer as it's closer to the edge of the board). Make sure not to castle into danger though.
Below are some games in which players develop well at the beginner level.