🚀 go-pugleaf

 For developing general purpose skills, I strongly recommend

 "Think Like a Grandmaster" by Kotov. 

 For developing end-game skills, I recommend 

 Chess Endings: Essential Knowledge by Averbakh.

 And after mastering the Averbakh book,

 "Rook and Endings" by Levenfish and Smyslov.

 Without a several hundred dollar investment in a chess library, 
 mastery of only these two books will make one a strong player.

 Of course, a careful and thorough study of opening theory is vital
 to playing the game a the highest level, and certainly important. It
 is also quite expensive to acquire materials. I recently (1 year ago)
 decided to give up competitive chess, and sold my chess library. At
 used book prices, I received a total of $400 for the books. I still
 had a dozen or so books to give away. I had accumulated these books over
 about 12 years of collection and study. To replace them with new books
 would cost in excess of $1000.

 Stick to the above two, and one can't go wrong.

 -Joseph Albert