Watch videos on fundamentals (i.e. chess principles to follow in various stages of the game; e.g. king safety in the opening)
After that, you should focus on basic mid-game tactics and end-game principles (you can ignore complex end-game theory, but basic king-pawn endgames should be learnt).
Play a longer time control (e.g. 15 | 10), and analyze each game you play thoroughly. If you do not learn from your mistakes, you are going to be stuck, but if you do fix them, your rating increases exponentially.
Following this can easily get you within the 1300-1600 range.
I've been playing daily for a couple of months. Seem to be stuck at 900ish. I do puzzles daily but can't seem to apply that stuff in the heat of it. There is no doubt that I need to study more, but I feel like I'm all over the place. Blunders abound. Sometimes when I review a game, the computer shows me a blunder that results in a loss of material say 3, 4 moves later. How am as a 900 player, playing similarly ranked players supposed to avoid those to improve?
It's confusing.