I have been a GM for many years and consistently get good ratings (back when the RPGA used to give them, from cons where that occurs and from random players at cons who often ask 'are you running anything else?' and from friends who I trust to be truthful). I always, always read GM advice information in pretty much every situation I see it -- online, in books, whatever.
I also am strongly involved in acting and direction theatre; a hobby that shares a lot of similarity with roleplaying (you could almost think of a role-playing group as an improv troupe performing for an audience of themselves, using a set of rules to focus their improv) and I cannot think of anyone in that profession who would not suggest reading advice. Even the great actors regularly do so.
GMing has a number of aspects, each of which can be improved on by even top-quality GMs. probably the top two in my experience are:
Creativity: How many books are there on creative writing? On world design? On building engaging stories? On well-developed characters? An engaging environment is so important for a good campaign that I will devour any advice available or this.
Dealing with People: The social aspect of a GM is also critical. You are effectively a team leader trying to make your team as effective as possible at their goal -- having fun. You need skills like handling problem players, encouraging shy players, managing stress points and issues that potentially hurt people.
A good advice book (or forum post) does not just state a single statement and leave it at that. It provides evidence, examples, personal stories and so on -- just like books on creativity or social skill do. There are
many books that offer just one piece of advice, and then spend the entire book explaining it.
Having said that, I will list a few things that have significantly helped my roleplaying:
Three descriptors per NPC: That will almost certainly make an NPC enough different from the others for them to be memorable. Advice on what those descriptors can be was very helpful too. Now I try and do this no matter what system I run in. Even a set of vanilla guards become much more engaging if they are "always talking about football • wearing uniforms that look years old • smell vaguely of beer".
Evil Hat's FATE ACCESSIBILITY TOOLKIT. For me, I have always worried that it I tried to present/play a character with a disability, that I would do a bad job -- minimizing the effects, stressing stupid things, overcompensating -- and this book, by presenting advice from people who have direct experience AND are role-players, was phenomenal. Tons of good individual advice, but more importantly gives me confidence that I can introduce characters with disabilities without looking like a dick.
Beat analysis (e/g Robin Laws' Hamlet's Hit Points). I've always sort known that you need ups and downs, and that the best campaigns mix them up, but having detailed careful explanations of why and how, with strong examples, makes it much easier to implement in practice.
... and a very specific example:
@CapnZapp's hate of several Pathfinder 2 mechanics. I like PF2 and generally disagree with him on a number of the issues. But I read pretty much all his posts because they and the responses challenge my experience with the game and that is always a good thing. It's easy to enjoy a game and so when someone says "X is terrible, don't do it" the initial response is "you are wrong; it works fine in my game" -- but a better reaction is to think "why don't I have that problem" -- maybe I haven't encountered it yet, maybe I just sort of ignore the issue, maybe I have developed a workaround in the way I apply the rules. Changes I have made based on these threads include better signaling of hazards, alternative presentations of haunts, modification of scenarios so rolling encounters are less likely or can be escaped from.
For me, advice snippets are rarely of any use (the "three descriptors" advice is an exception!). What typically makes advice work for me is an in-depth discussion. So I read books and I read threads, and when I remember to be open-minded about people's opinions, it is very common I learn something that makes my gaming better.
