Control the center
If you control the center, you control the board!
This provides more space for your side of the board.
Your pieces have more options to maneuver.
Early on, you should aim to develop pieces to challenge the center 4 squares and control the center!
A good goal is to control the center and move pieces that attack these 4 squares!
Nf3 - attacks 2 center squares: d4 and e5.
Nh3 - does not attack any center squares.