Next level

I was wondering how pass to the next level, I'm an autodidact, and is really hard to get better in this game, When i started to play I always investigated, How get better in chess?
And my search take me to different conclusions and ways to learn.
But today I found something, is truly what he say , in chess of today, the younger's in high levels maybe 2300 doesn't know what are supposed to they know, and younger people in low levels have a little knowledge, and the they not have habit to study, they never gonna let him reach all potential, and i say, i have to study more chess, but what type of books? maybe about endings or openings or middle game, or tactic, or strategy, but, what books are the best? And what better idea to get help, go to chess.com, to be guided.

So, what books do you recommend? To get more knowledge where are supposed to I have to have, guide me to be better, I don't know where start or what is more requeried in my level to pass the another one and the another one....and the another one.....and so successively