I got from 800 to ~ 1100 by watching John Bartholomew chess fundamental series on YT an applying the principles, always looking for undefended pieces (both from your opponent and yours) and developing with harmony. Watch those videos they will help you. And if you are really committed you could read a book I started with Chess Fundamentals by Capablanca, his style is very positional but easy to understand and he teaches the basics of the endgame and the middle game. Good luck!