I think it's not so different breaking 500 elo to 1500 to 2500. Everyone here is just asking the same type of question again and again and again and I think it's not that complicated.
The game is always the same and it always follows the same principles, you know, things like development, tactics, etc, and this principles such as tactics are further developed into concepts everyone has seen already, like forks, skewers, and so on. When it comes to tactics you only have to train your brain to spot a possible combination, calculate and get an advatageous position. It's that simple. Chess training is like 80% tactics.
Now, when it comes to opening theory, give it small time. Don't play 4 different openings per color, learn a few but strongly. About learning openings is not just knowing the order moves, it's about knowing your strenghts, your weaknesses, your plans and ideas, etc. My advice, learn any for white and 3 for black, 1 against e4, another one against d4/c4 and one against anything else. And this goes especially against low rated players, don't go sharp. Play solid. Don't play the sicilian because it has too much theory you need to memorize to end up in a decent position.
Dedicate more of your study to endgames. I personally hate pawn endgame puzzles because they are hard, they make you calculate a lot and since I'm mainly a blitz player I really need to excercise that with time pressure.
Some other comments I got:
- If you are suffering from time pressure, play with increment.
- Study games from great chess players. Understand what drives them, what's their reasoning, etc. Many of them made new opening theory too so that's a bonus.
- At least from my experience, rating fluctuation is pretty normal. You go up, visit a new rating objective, go down, and slowly make your way back up. It's been like that for me many times, even know I'm back to 2300 after 18 months of not reaching it. I've had my inactivity periods as well, but you get the point.
- If you are tilting, STOP PLAYING. It is that simple. Tilt is always under your control, emotional. If you are tilted, close chess.com, go grab water, take some air, do some chores but don't think about the losses. Come back tomorrow, check out your mistakes and keep moving forward.
- Understand your playing. Are you tactical? Positional? Do you like long slow games or aggressive sharp games? Do you like taking risks or you prefer being always balanced? Do you prefer closed or open positions? Do you use the knight or bishop better? What pawn structures are you familiar with? Etc. Know what you do, your weaknesses in the position and your advantages. This helps not only for openings but for the mind game in general. Make chess enjoyable for you.
I think that's all. Excuse my bad english. To my experience there's only one way to reach any elo goal, it's to keep playing, reviewing your mistakes, learning the patterns on opening theory, tactics and endgames and if you understand the whys of your moves you'll get better. Don't move for moving, have an intention. Reason your moves.