Learn an opening. My favorite is the Italian!

The rule of always looking for Checks, Captures and Threats. Can you check their King? Can you do it in a way that gets you something beneficial? Can you take a piece? Can you safely threaten to do so? Some slowly played games against the computer will help you a ton.

first, Learn the London as white and modern defence with e3 as black. Or take a pick at an opening for both sides. Do not play anything else. Do not try to learn a hundred moves in a hundred openings, stick to one. Just one.

Actually study the opening. (just keep on playing it in the meantime.) Take advantage of common mistakes.

Second, When behind: keep playing the entire game. Do not quit. Do not give up. Do not surrender. Your opponents most likely do not know any endgame tactics.

When ahead: Get rid of everything, exchange everywhere, every opportunity to trade, take it. Get to the endgame asap.

Third: Puzzle. Puzzle. Puzzle.

Fourth: Watch high level commentary on high level games a lot.

Fifth. Analyse yourself. What did you miss? Where was the game turned around?

You’ll probably need to study some theory on openings and endgame.

Also do puzzles to improve your tactics.

Switch to lichess.org (open source, has all of chess com’s paid features available for free, plus no ads or trackers).

Start with the chess basics set: https://lichess.org/learn

Then the basic tactics set: https://lichess.org/practice

And then do puzzles: https://lichess.org/training (chess com makes you pay for more than a few per day). Do a lot of them.

Then, you can also analyze your games on lichess using it’s analysis engines (which chess com makes you pay for). Uh I can’t find a good guide how to do this right now, check back later.

The single player campaign is pretty good

600-700 is around when the basic beginner traps stop working. Fried liver attack, etc, and not moving on past those traps is why so many get stuck there for too long.

Reading theory is helpful, but I’d say that’s more important at 1000+ ELO. For now, I’d say learning the basics of evaluating any position (king safety, long diagonals, weak squares, etc). Also, knowing many openers is good and all, but I suggest picking one and get really good at that. “I fear not the man who has practiced a million openers once” -Bruce Dickinson, or something.

My personal choice for openers are Kings Indian attack (as white) or Pirc Defense (as black). These are very similar, so if you know those two well, it doesn’t really matter what color you start as - they tend to end up with similar mid-games.

Also, around 700 it becomes important to spot which tactics are available to you in various positions. The puzzles at chess.com are really helpful for learning this.

As for the lichess argument, yes, it’s good. But I find that the analysis engine on chess.com is slightly better. And on that note, if you have a subscription, analyze your games afterwards, as it helps you understand what went wrong or right (yes, don’t just analyze your victories). Also, keep in mind that chess.com and lichess have different ways of calculating ELOs.

Also, use the time you have. If you’re playing 10min games, make sure to use your time accordingly. Don’t rush into a blunder because you didn’t see the revealed check or the fork. Personally I mostly play 10min games, as that gives me plenty of time to evaluate the board. Sometimes I do 3min when I’m less patient.

Source: 1757 day streak on chess.com, 1261 ELO while I’m writing this (Although, knowing myself, I’ll trip back to 1100ish soon)

Warm up with puzzles before playing.
Stick to a repertoire you’re comfortable with and your opponents are not.
Play when your mind is in the right place and focus properly.

Play in real life.