Best way to improve your game?

Study games of Morphy, Chigorin, Marshall, Anderssen. You will learn Development, Tempo, Tactics and Checkmating.

Only if they already have a good enough understanding of the game to determine why the GM's made all of their moves.   When I was a 1400-1500 player, I didn't understand most GM games.   You should watch some video lessons on YouTube for a few years first.   Then maybe "graduate" to watching GM games, with commentary, after you are about a 1700-1800 player.

Wait till 1700? I suggest studying Old Master's games as you hit 1200s in chess.com.

At 1700 it's time to study Capablanca, Rubenstein then Tal. 

Imitating the games of attacking players will only get you so far though.   Defense is just as important as offense.   If you're a 1200 player, you won't know why Capablanca made a particular defensive move or chose to play a boa constrictor type of opening.   Also, when someone plays a better move than their opponents did (which happens very often these days), you won't know how to proceed with your attack.   Those old Masters were playing against weakies, compared to the modern GM's.   I'd much rather study a Carlsen-Liren game, a Kasparov-Karpov game or a Fischer-Spassky game than Capablanca vs Joe Blow.   But you'll have to be at least a 1700-1800 player to fully understand them.

At 1700 it's time to study Defense. Capablanca and Rubenstein are the Pioneers of defensive chess and winning Endgame. Tal attacking games show strong defense aren't a solid fortress after all.

True. Morphy and company destroyed the Weakies. So I recommend it to 1200s players. If they can't destroy their peers at 1200, they would never move upward.

https://www.chess.com/blog/2Bf41-0/positional-elements-in-action-3-important-queen-moves

" But you'll have to be at least a 1700-1800 player to fully understand them."

Yes, indeed! I suspect you might need to be rated as high as 1750 before you fully understand every nuance of a Carlsen-Liren game. Those guys don't mess around! But a 1300-player should have no trouble grasping every detail of the games of Capablanca and Rubinstein. Mere child's play!

"... Batsford's new edition of Logical Chess: Move by Move, written in 1957 by Irving Chernev, is a collection of 33 games with a famous player on at least one side of the board. ... In many ways, it would [be] a wonderful 'first' book (or first 'serious' book, after the ones which teach the rules and elementary mates, for example), and a nice gift for a young player just taking up chess. ..." - IM John Wstson (1999)

https://theweekinchess.com/john-watson-reviews/assorted-recent-books

1) What are the best books (reads) for new players to improve their game. 2) Just, give a list of your books, chess, in your library.

Maybe so.  To be honest, I've never studied those two players' games much.   I think I played through one Capablanca game.   I remember loving how he controlled the chessboard and took space away from his opponent.  

My two favorites were "How to Reassess Your Chess" by Jeremy Silman and "Pawn Power in Chess" by Hans Kmoch.   There are several other good ones that I've skimmed through, but I forget the names of them.

People like Kasparov, Fischer, and Carlsen have dozens of Capablanca games and Morphy games, and Rubinstein games memorized. If they're not to good to learn from those giants, why would we be?

I have been able to improve my rating by 350 points in the past 6 months, but this is because I play longer games. The longer I think for the better I seem to get. Most of the games I play are 30 minutes long.

Well, it's a good novice to intermediate book then.  I learned a lot from it when I was a 1400 player.

Then I must be better than I think I am.     

"How to Reassess Your Chess, 4th Edition was designed for players in the 1400 to 2100 range." - IM Jeremy Silman (2010)

https://web.archive.org/web/20140708095832/http://www.chesscafe.com/text/review769.pdf
https://www.silmanjamespress.com/shop/chess/how-to-reassess-your-chess-4th-edition/

"... how many chess games can you replay (till the end) ..." - VimalKumarK

"I couldn't replay any although I could recognise quite a lot." - CM JamesColeman

"Good point. I could have replayed that one. Also Reti-Tartakower where White sacrifices his Q on d8 and then forces mate with a double check. So maybe 2. Both of those are rather short though." - CM JamesColeman

"Oh yeah, that one. Maybe 3 then " - CM JamesColeman

"There are many many must-know games for general ideas and themes but not sure of the practical value of having all of them memorised move by move all the way through to resignation?" - CM JamesColeman

"I don't think you have to have them memorized. Just playing them over, even fairly quickly will help put the patterns and ideas into your head." - Morphysrevenges

"Yes, agree with you entirely Morphysrevenges, but the OP was asking about memorised games that you can replay out at will. For me at least, that's not many." - CM JamesColeman

Games mentioned in the January 7, 2017 discussion:

http://www.chessgames.com/perl/chessgame?gid=1233404

http://www.chessgames.com/perl/chessgame?gid=1250654

http://www.chessgames.com/perl/chessgame?gid=1259009

http://www.chessgames.com/perl/chessgame?gid=1224575

http://www.chessgames.com/perl/chessgame?gid=1132699

http://www.chessgames.com/perl/chessgame?gid=1132581

Like I said before, I got a lot out of it.   I was around a 1450 player when I first read it and I believe the lessons I learned turned me into a 1600 player.   I don't remember any of it being "beyond my pay grade".   I also read the sequel.   I think it was called something like "How To Reassess Your Chess: Workbook".