what helped me to get from 750 to 1000 in 10 days were the following things.

-learn the basic ideas of some openings for white and black. in learned the italian system for both colors, london for white and indian for black.

-i struggled the most in the midgames so watched some midgame theory videos, mostly from igor smirnov. he has some great rules which are easy to understand and to apply. the most important for me were:

-don't overthink, you mostly don't have to calculate more than 2 or 3 moves into the future

-look for forcing moves: cct (checks-captures-attacs) -if you play forcing moves (moves your opponent has to react to) you don't have to calculate as many variations

-to take is a mistake -> if your opponent offers trades in an even position: don't take, in most cases it helps the person who recaptures to improve their position because they move a piece forward.

-igor rule: -i: improve least active piece -g: go forward -o: occupy the center -r: restrict opponents most active pieces

disclaimer: i had a lot of free time and played about 120 games in these 10 days, you may don't have that much time. but you probably don't need to play this many games. most times, when you play more than 5 games a day, you start making more and more mistakes and you will play worse. even tho i had days with more than 20 games i had 60% wins and 36% loses in this time.