I donwload them all for free and read what I want. Do the same. Read a good book on strategy, a good book on tactic, a good book on analysis, a good book for solve exercises, and, if you really want it, a good book on openings. "Study them thouroughly"! General books. Don't buy a book on the Sicilian Dragon, but a serie like "Mastering the chess openings" (John Watson) that covers all main openings and their principles. Well, I don't know if this will work with you, but with me it's working.
I have over 45 chess books but I don't understand a single one of them
The books I currently use for training are the entire Build, Boost, Evolution course by Yusupov; I also study "Pawn Structure Chess" By Andrew Soltis for the middle game, "Mark Dvoretsky's Endgame Manual" for the endings(currently only the blue diagrams), "Think Like a Grandmaster" by Alexander Kotov for calculation and "500 Master Games of Chess" by Tartakower and Dumont for analyzing annotated master games.
I haven't found a good book for hammering down opening principles. Not simply a repertoire book but purely something to practice the opening principles. It's a weakness of mine according to the Yusupov series, in the first book it's the only section I barely passed.

"How to Reassess Your Chess, 4th Edition was designed for players in the 1400 to 2100 range." - IM Jeremy Silman (2010)
A 1400 USCF-rated player has usually played in a couple of rated OTB tournaments. So that player would have played a bunch of serious games at a slow time control and would be considerably more advanced than almost any player rated 1400 on chess.com. I don't think a the average 1400 USCF player is really quite ready for "How To Reassess Your Chess," But I'm completely sure that most players rated around 1400 on Chess.com aren't
I read it at 1400 and I got a lot out of it, but I was probably more well-read than a less active 1400 Chess.com player.

... a serie like "Mastering the chess openings" (John Watson) that covers all main openings and their principles. ...
Can you tell us where it covers 1 e4 e5 2 Nf3 Nc6 3 d4 exd4 4 Nxd4 ?

I just got chernev's most instructive games and I gotta say I love that book. I just went through the first game and it was actually a pleasure. Not like Kasparov's modern chess where there are like 40 moves deep annotations on move 6.
The first game was the famous Capablanca rook endgame game where he sacs two pawns in the ending to get a dominating position. Pretty cool. Never studied the whole game before.
.., or De La Villa's 100 endings you must know. ...
"... 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

Find a new hobby. Unless you have absolutely nothing better to do than read chess books. That's probably not possible. I'm half joking. You only need to read Fischer's My 60 memorable games and go over with engine assistance. You can also analyze GM games at top level with engine assistance too, and try to go over trees of variations. I think at one point I owned 80 books and read maybe 4 of them.
... the entire Build, Boost, Evolution course by Yusupov; ....
http://www.qualitychess.co.uk/ebooks/Build-up-Your-Chess-1-exceprt.pdf
https://web.archive.org/web/20140708103321/http://www.chesscafe.com/text/review699.pdf
http://www.qualitychess.co.uk/ebooks/Build-up-your-chess-2-excerpt.pdf
http://www.qualitychess.co.uk/ebooks/Build-up-Your-Chess-3-exceprt.pdf
https://web.archive.org/web/20140708103659/http://www.chesscafe.com/text/review778.pdf
http://dev.jeremysilman.com/shop/pc/Boost-Your-Chess-1-77p3744.htm
http://www.qualitychess.co.uk/ebooks/Boost-Your-Chess-1-excerpt.pdf
http://dev.jeremysilman.com/shop/pc/Boost-Your-Chess-2-77p3745.htm
http://www.qualitychess.co.uk/ebooks/BoostYourChess2-excerpt.pdf
http://dev.jeremysilman.com/shop/pc/Boost-Your-Chess-3-77p3746.htm
http://www.qualitychess.co.uk/ebooks/BoostYourChess3.pdf
https://web.archive.org/web/20140708103149/http://www.chesscafe.com/text/review834.pdf
http://www.qualitychess.co.uk/ebooks/Chess-Evolution-1-excerpt.pdf
https://web.archive.org/web/20140708085817/http://www.chesscafe.com/text/review843.pdf
http://dev.jeremysilman.com/shop/pc/Chess-Evolution-2-77p3643.htm
http://www.qualitychess.co.uk/ebooks/Chess_Evolution_2-excerpt.pdf
http://dev.jeremysilman.com/shop/pc/Chess-Evolution-3-Mastery-77p3753.htm
http://www.qualitychess.co.uk/ebooks/Chess_Evolution_3-excerpt.pdf
http://www.qualitychess.co.uk/ebooks/QandAwithArturYusupovQualityChessAugust2013.pdf
https://www.qualitychess.co.uk/ebooks/Revision&Exam1-excerpt.pdf
... "Pawn Structure Chess" By Andrew Soltis ...
https://web.archive.org/web/20140708101523/http://www.chesscafe.com/text/review908.pdf

for Endgames I am thinking of gettings this:-
https://www.newinchess.com/media/wysiwyg/product_pdf/7742.pdf
BoilingFrog,
For intermediates isn't it inadvisable to use chess engines.
... "Mark Dvoretsky's Endgame Manual" ... (currently only the blue diagrams) ...
"... before discussing the specifics of Dvoretsky's Endgame Manual ..., a word of warning is in order. I must emphasize that this is a terribly advanced work that I don't think is a very good way for the average player to study the endgame. ... That said, if you are up to a real challenge and have a great deal of time to devote to reading and playing over examples you will inevitably derive great value from this work. ... In my own teaching to average players I am still using Mueller and Lamprecht's Fundamental Chess Endings, which has a wonderful balance between Encyclopaedic coverage (I can find almost anything), examples that can be shortened at most points, and clear explanations that bring together endings of the same sort. ..." - IM John Watson (2005)
http://theweekinchess.com/john-watson-reviews/the-end-game-comes-before-we-know-it

chess books I think should be for enjoyment. If you enjoy chess and reading and playing over games why not? Find a chess book that you actually enjoy, its half the battle. It probably doesn’t matter what it is as long as you are exposing your mind to different types of positions and you are actively engaging in analysis and enjoying it. If you don't enjoy it, try another until you find one that you do enjoy. All chess games have a narrative.
... I haven't found a good book for hammering down opening principles. ...
"... For beginning players, [Discovering Chess Openings] will offer an opportunity to start out on the right foot and really get a feel for what is happening on the board. ..." - FM Carsten Hansen (2006)
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf
... a serie like "Mastering the chess openings" (John Watson) that covers all main openings and their principles. ...
Can you tell us where it covers 1 e4 e5 2 Nf3 Nc6 3 d4 exd4 4 Nxd4 ?
drmrboss wrote: "Scotch opening, (C40-49, I think)"
Know of a volume and page number in the Watson series?
I just got chernev's most instructive games and I gotta say I love that book. I just went through the first game and it was actually a pleasure. Not like Kasparov's modern chess where there are like 40 moves deep annotations on move 6.
The first game was the famous Capablanca rook endgame game where he sacs two pawns in the ending to get a dominating position. Pretty cool. Never studied the whole game before.
"... Just because a book contains lots of information that you don’t know, it doesn’t necessarily mean that it will be extremely helpful in making you better at this point in your chess development. ..." - Dan Heisman (2001)
https://web.archive.org/web/20140626180930/http://www.chesscafe.com/text/heisman06.pdf
"... The books that are most highly thought of are not necessarily the most useful. Go with those that you find to be readable. ..." - GM Nigel Davies (2010)
"... If it’s instruction, you look for an author that addresses players at your level (buying something that’s too advanced won’t help you at all). This means that a classic book that is revered by many people might not be useful for you. ..." - IM Jeremy Silman (2015)
https://www.chess.com/article/view/the-best-chess-books-ever
for Endgames I am thinking of gettings this:-
https://www.newinchess.com/media/wysiwyg/product_pdf/7742.pdf ...
https://chessbookreviews.wordpress.com/2018/02/01/eat-your-oatmeal/
That's dynomyte!!! Outta sight!!! OH YEA BABY!!!
And another fresh account bites the dust ...