Forget openings for now. Especially memorizing moves without understanding the reason behind the moves. At your level its all about opening principles, tactics, double checking your moves, and asking: "What is my opponent trying to do?"
Study all the basic tactical motifs like pins, forks, skewers, etc.
Knowing all motifs is useful, yet the double attack is what happens most often... and the reason behind several "surprises" in beginners' games.
The probable reason is that most double attacks often target material that is not in the same cluster of pieces, thus out of the beginner's "attention".
I am currently about 1200 on chess.com, although I believe I am actually 1000.
What tactical motifs should someone at my level focus on? I had trouble memorizing openings so I gave up on that for now.