how to improve my game

Play longer time controls, Less playing Blitz, more playing Standard games!
Review your games, especially your losses and analyse where you went wrong. Note down in another document if the game was decided by a blunder or lots of inaccuries, not playing aggressive enough etc. and note down other notes of games in this document as well.
You can analyse where your problems are, do you often have inferior positions? Then you need to work on your positional chess, for instance the free Chess mentor course on chess.com can help a lot and otherwise the forums has enough materials to get better at this aspect of the game.
Do you blunder often? Then you need to get better at tactics and practice 5 to 10 tactic puzzles a day online, preferably more if you want to get better faster.
Then you need ask yourself if you know what to do in the endgames you encounter. If you don't always know what you are doing then you need to learn some basic endgames. Learning endgame technique is often a quick way to improve when at the lower levels (counts for me as well).
Possibly helpful:
Simple Attacking Plans by Fred Wilson (2012)
https://web.archive.org/web/20140708090402/http://www.chesscafe.com/text/review874.pdf
https://www.newinchess.com/Shop/Images/Pdfs/7192.pdf
Logical Chess: Move by Move by Irving Chernev (1957)
https://web.archive.org/web/20140708104437/http://www.chesscafe.com/text/logichess.pdf
The Most Instructive Games of Chess Ever Played by Irving Chernev (1965)
https://chessbookreviews.wordpress.com/tag/most-instructive-games-of-chess-ever-played/
Winning Chess by Irving Chernev and Fred Reinfeld (1949)
https://web.archive.org/web/20140708093415/http://www.chesscafe.com/text/review919.pdf
Discovering Chess Openings by GM John Emms (2006)
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf
Openings for Amateurs by Pete Tamburro (2014)
http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html
Chess Endgames for Kids by Karsten Müller (2015)
https://chessbookreviews.wordpress.com/tag/chess-endgames-for-kids/
http://www.gambitbooks.com/pdfs/Chess_Endgames_for_Kids.pdf
A Guide to Chess Improvement by Dan Heisman (2010)
https://web.archive.org/web/20140708105628/http://www.chesscafe.com/text/review781.pdf