I think the majority of titled players had a coach or trainer at some point. That and they looked through GM games and analyzed their own games WITHOUT a computer.
Personally as a class A player I think reading Silman's the Amateurs Mind, Silman's Complete Endgame Course, and doing as many tactics in 303 tricky chess tactics and 1001 Winning Chess Sacrifices and Combinations as I could per day are what have improved me the most.
Good luck.
I have a question that I would like to direct to titled players from NM on up...
When it comes to studying chess what is the one area that you feel most improved your game?
A lot of time I'll see people post that it was tactics. Or that it was positional play. Or that it was opening theory. Or whatever. But the people who post those things tend to be mostly class players like myself.
So I'm wondering what it was that the more advanced players here did that helped them the most to improve.
Specifics would be nice if possible. For example "I studied tactics. I did at least 20 puzzled each day." Or "I played through at least three annotated GM games per day." Or whatever.
Also, since these days I feel compelled to add a disclaimer, please ignore my rating on this site. I'm 1500 USCF. A lot of times when I post in threads I get a chorus of "just learn to stop dropping pieces and learn beginner tactics rookie" style comments. I'm willing to stiplate that I am indeed a rank amatuer, but that would be the rank of a class C player, not an E...