Stuck at 775

How do I improve?

you have to do more puzzle

Do lessons and try to stick with the basics

Do lots of puzzles and lessons

If you have chess.com premium go to puzzle themes and just switch on basic tactics that you need to know

Discoveries, pins, forks, skewers, back rank, maybe even throw in a mate in 2 if you want to. If you don’t have premium, go to chesstempo.com since I’m pretty sure there is a feature there that lets you pick by theme.

do this and I’m sure you’ll improve

After looking at your profile:

1) It seems that you may win considerably more often with the white pieces. With this, perhaps you can study the fundamental moves of the Scandinavian Defense or the King's Indian Set-up. As one who passed 800 ELO a few weeks ago, these seem to often get your opponent more out of their comfort zone, which you can use to your advantage.

2) Although you do play Rapid games, 15|15 may be too quick for being able to sufficiently think though tactics and strategy. Personally, I would play at least 30|0.

3) Others have also been stating in this thread that doing puzzles can help with improving at chess. There's a whole bunch of sites where you can play puzzles for free, including those aforementioned along with Lichess and the free tactics courses on Chessable.

I’m about to get premium so this could help

#1
Always check your intended move is no blunder before you play it. Hang no pieces, hang no pawns and you are 1500.

Improving Your Chess - Resources for Beginners and Beyond...

https://www.chess.com/blog/RussBell/improving-your-chess-resources-for-beginners-and-beyond

You are playing too fast for sure. At least you do in most of your games. Finishing such game with 12, 13 minutes on the clock or even more time than when you've started means that you would probably benefit a lot from taking more of your time while playing.

Aim to spend more time, especially on critical moves (when you are about to capture something, or when you might change the pawn structure, AKA when you have the option to take the pawn, push the pawn or leave the pawn alone). In general, it would be good to finish your games with less than half of your time remaining on the clock, except for some really short games you win.

Have you tried attacking or check mating your opponent’s king?

I lost this tournament game after missing a mate in two after a brilliant move/rook sacrifice to start the sequenced coined by chess.com 

Worst is missing mate in one even the queens off the board.

https://www.chess.com/game/live/39215365235

https://www.chess.com/game/live/39236360667

I have a tendency to give the game back to my opponents more than I would like.

Shoot now and ask questions later.

I'm not the very high rated but I think if you're less than 800, you can improve by not blundering, learning commonly used openings and rook endgame patterns.

After a year I finally got to 900. This is what I did. (I only play rapid)

Do puzzle Rushes & regular puzzles

Play bots (to practice not blundering)

Learn two openings and always use them (eg White = London, Black = pirc). (Get to middle game unscathed.)

The 800s are straightup Blunderland. If you can get thru a game w/o blundering and snatching unprotected pieces you will rise. WIth that said I have a feeling "real" chess starts at around 1200 people at this level would eat me alive...

Completely agree, for me, nearly all of my games are either won or lost by a forced checkmate blunder or hanging a valuable piece. I also play the London system with white, though I'm interested in how you're doing playing the Pirc. I've studied it decently without much success.

sit on your hands.

Along with puzzles, use your time in games efficiently. Do not race through the opening, consider your moves. Always look at the board, calculating tactics etc. When you get into higher elos, your going to have to calculate instead of basing it off of intuition. 15|15 is great, but use your time. You shouldn’t be ending the game with the time you had at the start. The KID and the scandi are very good, and as said above, your going to get your opponents out of their comfort zone. Practice board vision, when practicing tactics calculate all the way through, etc. 

As always, learn from your mistakes. 

So one could argue this is the best info for me?

Hi! I've been training students for 5+ years and they have achieved great success. If you're interested, consider DM me and we can take it from there.

Puzzles and try to spot tactics. Only Rapid. 30 mins or 15 mins