How to improve!
There are three areas to work on, Openings, Middlegame Strategy and Tactics, and Endgames.
Tactics is most important.
Work on the Tactic Trainer here and at chesstempo.com. After you solve each problem, decide which tactical motif was used and check with the TAGs listed for each one. Go back over the problem and study WHY you missed the pattern. You should slowly learn to be able to demonstrate any of the several dozen tactics at these interactive sites:
https://www.chess.com/article/view/chess-tactics--definitions-and-examples
https://chesstempo.com/tactical-motifs.html
Your tactics progression can also involve books on the middlegame. The first edition, around 200 pages, of Silman's How to Reassess Your Chess is better for those at the just-past-basic-improvement level than his 638 page 4th Ed. You also need a good book on Opening Principles, like Evans et al's How to Open a Chess Game and a good book on Endings like Jesus de la Villa's 100 Endgames You Must Know.
Do you understand the importance of the center, developing pieces, castling?
These are the tactical weapons and strategic concepts that are critical to playing well.
Understanding these is fundamental to solving the tactical motifs mentioned by MickinMD above. It will also increase your love of the game as you gain a greater depth of understanding of the tools at your disposal.
MickinMD’s suggested books and others will help u gain the knowledge u may be missing.
And play, play, play.
"How to Reassess Your Chess, 4th Edition was designed for players in the 1400 to 2100 range." - IM Jeremy Silman (2010)
I have often seen praise for How to Open a Chess Game, but it should perhaps be mentioned that, having been written about four decades ago, it used descriptive notation (1 P-K4 P-K4 2 N-KB3 N-QB3 etc.). Also, the reader should perhaps be warned that, apart from Evans himself, none of the GM authors "was given a specific topic or assignment." For more overall organization, one might want to turn to a book by a single author, such as Discovering Chess Openings by GM John Emms (2006)
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf
or Openings for Amateurs by Pete Tamburro (2014)
http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html
https://chessbookreviews.wordpress.com/tag/openings-for-amateurs/
https://www.mongoosepress.com/excerpts/OpeningsForAmateurs%20sample.pdf
or Winning Chess Openings by Yasser Seirawan (1999).
https://web.archive.org/web/20140627132508/http://www.chesscafe.com/text/hansen173.pdf
"... the 2000+ player for which 100 Endgames You Must Know is really intended ..."
https://web.archive.org/web/20140708105702/http://www.chesscafe.com/text/review645.pdf
Possibly of interest:
Simple Attacking Plans by Fred Wilson (2012)https://web.archive.org/web/20140708090402/http://www.chesscafe.com/text/review874.pdf
http://dev.jeremysilman.com/shop/pc/Simple-Attacking-Plans-77p3731.htm
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 (1948)
https://web.archive.org/web/20140708093415/http://www.chesscafe.com/text/review919.pdf
Back to Basics: Tactics by Dan Heisman (2007)
https://web.archive.org/web/20140708233537/http://www.chesscafe.com/text/review585.pdf
https://www.chess.com/article/view/book-review-back-to-basics-tactics
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
Silman's Complete Endgame Course
http://theweekinchess.com/john-watson-reviews/theres-an-end-to-it-all
https://web.archive.org/web/20140708103149/http://www.chesscafe.com/text/review594.pdf
A Guide to Chess Improvement by Dan Heisman (2010)
https://web.archive.org/web/20140708105628/http://www.chesscafe.com/text/review781.pdf
Studying Chess Made Easy by Andrew Soltis (2009)
https://web.archive.org/web/20140708090448/http://www.chesscafe.com/text/review750.pdf
Seirawan stuff:
http://seagaard.dk/review/eng/bo_beginner/ev_winning_chess.asp?KATID=BO&ID=BO-Beginner
http://www.nystar.com/tamarkin/review1.htm
https://www.chess.com/article/view/book-review-winning-chess-endings
https://web.archive.org/web/20140708092617/http://www.chesscafe.com/text/review560.pdf