The writing world is full of advice: agents, editors, fans, authors, and wanna-be authors all have advice on everything from plot to query letters to marketing. It becomes daunting just to read it, much less act on it.
You need to know what people are saying. Some of them know what they're talking about. Some don't, but they'd never admit that. I once heard a speaker proclaim to a roomful of hopefuls that one should NEVER send a query by email. He insisted that a snail-mail letter with a stamp proved to an editor or agent that we were serious about our craft. Can you say, "living in the last century"?
Of course if it's an agent or editor giving advice, it's worth a listen, but even there we have to remind ourselves that it's one person's opinion. One says, "Never send me a synopsis," the next says always send one. Listening to advice from the pros means sorting them into their categories and not assuming that one adviser fits all.
The same is true for authors. We're vastly variant, which is a good thing. But it means that what works for me may not work for you. I spoke to a group of writers last week and was asked how a query letter should begin. Quick answer? I don't know. I can only tell you how I begin mine, and I've been wrong hundreds of times, judging from the rejection letters in my files.
Then there are on-line advisers: blogs, articles, etc. Great stuff, lots of the time. Especially for beginners, such sources give the basics, point out pitfalls, and give tips that save time, energy, and even embarrassment. But it's one person's experience, and that person may be in a different genre, a different dynamic, a different place in the "journey" of publishing than you are. Marketing advice is useless until you've written that winning query letter, and query advice is pointless until you've got that MS in tip-top shape.
The question with advice to writers is the question with advice in general: how much do we let it influence us? We know from living to adulthood that much of the advice we get is thoughtless and wrong. I've found that when a sentence starts with "You should..." I can pretty much stop listening. Better is advice that begins with: "This is how I do/did it." Even then, each person has to take what works for her and apply it. Each day I skim through the advice I've "asked for" on line, filing away tidbits that may be useful in the future, and forgetting the rest. The same is true when I hear speakers at conventions or talk with other authors. When someone says I MUST greet each person at my book signings with a question like, "Do you read mysteries?" I think, "That's not me." Other times I get veritable jewels of advice, and those I mull over, write down, and act on as soon as possible.
So my advice on advice? (What a concept!) Learn what you can learn, take what works for you, and don't let yourself worry about the rest. Lots of what we get is great advice, possibly. It's just not great advice for you.