Fortunately we have many great pool instructors available today. That said, imo there is no better way to learn than by OBSERVATION! By that I mean watching closely what the top players are doing and studying it. Nothing better than watching the best players Youtube videos and absorb what works for them and how they go about it. After that, Copy, Copy, Copy what you see! Learn how to do it and you will be a better player, Guaranteed!
Additionally, being schooled by a top flight instructor should help you work out some kinks in your game, both mentally and physically. In my experience none better than the aforementioned Nick Varner and Ray Martin for articulate and simple tips on how to refine your game. No one better than Jerry Breisath and Mark Wilson to help with any fundamental flaws in your stroke or stance. All the others mentioned here are or were good instructors. Miz was sharp as a tack and really knew his stuff. One man who is glaringly omitted so far is Bert Kinister. He created the most extensive library of instructive pool videos ever assembled. A wealth of knowledge there! Plus Bert was a master of the mental game. He knew how to motivate a player to elevate his game to a higher level. He took Niels from being a journeyman pro to the top of the heap! See post #46 for his photo.
I hesitated to add this, because it sounds like I'm bragging, but I will anyway. I'm proud to say that I played a part in the success of several players, most notably Tang Hoa and Dennis Orcollo. Very little to do with the physical part of the game, much more to do with the mental side of being a winner. There have been several others that I prodded to achieve their goals with a simple word or two at the right moment. Once upon a time a very young Shane came to me and asked me if I thought he could ever be a top player. My response to him was that there is always room at the top if you're good enough. That's all he needed to hear!