Intro
As a beginner, you should be familiar with the basic rules of chess, but to really improve to the next level, which is from 1000 - 1300. In my experience, I think are two main areas to focus on: opening principles and checking for tactics.
Opening Principles
The opening isn’t difficult, just develop all your pieces, right? There are actually a few more key heuristics you should use such as not moving too many pawns, not developing your queen too early, and prioritizing castling.
Mistake #1: Not developing your pieces
While this position is equal, if white neglects the king's safety in favor of trying to create something in the middle of the board, practically speaking, black will more likely win this game.
Mistake #2: Moving too many pawns
h6 is slow, giving white a further lead in development.
Tactics
Most 1000 to 1300 easily miss tactics such as forks and pins. Practicing them with chess.com or lichess.org puzzles will greatly improve your ability to spot them when attacking or identify what your opponent’s intentions are for a move.
Fork
Pin
A classic trap out of many Italian/Philidor Defense positions, where black greedily takes a pawn, gets his knight pinned by to the king by white rook, and then the defending pawn is pinned to the Queen.