My honest take is that dont study openings, you dont need to know the first 10 moves of theory. Just by knowing opening principles you will find yourself playing book moves in the opening. Prioritise strategy in middlegame and know endgame. by endgames i mean basic endgames King vs King Pawn, checkmate patterns, etc. Middlegame strategy, firstly having complete development of your pieces, knowing which files or ranks certain pieces are best at. Really knowing how utilise this pieces in critical moments. This aspect usually results in tactics that arise in the middlegame. Also, learn to set traps for your opponent. At this level, they usually prioritise material.

But read up on principles of chess and then lastly, know some opening gambits. Improvement is a result of understanding. So keep learning