All GM advice can be good or bad depending on how it’s taking.
Nah. There's some advice that's purely bad, unquestionably bad.
Whether there's some advice that is always good/useful is uncertain, but there is definitely advice that is purely negative, and only delusions prevent people from realizing it. It's a lot less common now, in 2023 than it was when the internet was dawning in 1993, of course. Back then, absolutely terrible advice was absolutely rife. It was a constant.
For example, I remember reading a screed once in the mid-late '90s about how DMs had to punish characters in-game for decisions the players made in order to show them who is the boss - i.e. if a player pissed you off, kill off their PC. At the time, lots of people claiming to be experienced DMs were agreeing with this! Indeed, you still sometimes see stuff a bit like this alongside "The DM is God" suggestions.
There's also the classic prison-logic "kill a PC early on to show you mean business", which is just not good advice on any level.
Gary Gygax's terrible book Role-Playing Mastery (which even he later disavowed!) is absolutely full of this sort of stuff and has quite a lot of generally bad advice.
Coming from a place of ‘this will work for everyone’ generally raises my suspicions.
The trouble is that's an awful lot of advice - or rather it used to be - just absolutist "this way is the only way" stuff.
Personally I think the advice I find most troubling is stuff new DMs will take on board because it sound innocuous -
@TerraDave gives a good example here:
Anything that says the DM should work more (versus good advice, which tells them how to do more with less time).
Back in ye olden days, this meant a bias for home-brewing over using modules, as they were called (even though there were excellent modules available, and people played them). Later it might mean creating an elaborate sandbox, or really trying to understand your players and going out of your way to cater to your players (though this can bog the campaign down and, in various ways, actually annoy those players).
There are other examples, many, of "here is all the extra work you can do to be a better DM".
I think those examples are fairly mild, too. I've seen nonsense like "You get out what you put in, so the more work you put in, the better the game will be!" repeated, particularly by what I'd consider "mildly experienced" DMs - like ones who've been playing 3-10 years but not decades. It's funny because the same people will often advise against spending too much time on writing lore, but will then suggest incredibly high-effort prep methods, or will argue against homebrew adventures, but then suggest taking more time than it takes to write one to modify/tweak/fix a WotC adventure.
