The second draft can be shittier than the first
Particularly if it's your first work and you decide to follow all that advice everyone is falling over themselves to give you. It's not always the case, but it's possible. Just make sure you keep a copy of that first draft - the naïve and childlike and imaginative one you wrote before the over-worked Frankesteinian monstrosity you're currently wrestling with.
Following the rules can make your writing flat and formulaic
You can show rather than tell, start in media res, remove all exposition and backstory, strip all purpley description, give your characters goals and motivations and your scenes conflicts and it will still read like a rejected script for Eldorado. There's no trick to this – writing is not science, it's alchemy. And when you do finally turn that lead into gold, you'll probably have no bloody idea how you did it.
Revising can kill your originality
People know what they like, they know what they think is good writing - and it's not yours. It's the stuff that the establishment picked up on and the rest of the world followed. And your critique group are going to want to make you write like that. And if you follow all the advice they give you, you're going to end up with that Frankensteinian piece of shit that I mentioned earlier, with nothing of you and your originality left in it. Emulation is good, but there has to be a certain amount of 'fuck you' too. So when you revise, make sure it's your story you're revising, not somebody else's.
Flaws are like bad memories
You forget them and remember the good bits. If readers are swept away by the romance, the milieu or the story they won't care about too many adverbs or too much telling or backstory or whatever. No one says Tolkien has too much backstory; no one cares that Harry Potter is awash with adverbs, millions of readers don't give a toss that the Twilight series is one epic expert-writing fail. Do what you do and do it well.
You can't be taught, you have to learn
Don't get me wrong, I'm not against the rules. I devour them – but I do it in order to know them in the hope that I can master them, and one day be free of them. I've nothing against writing experts – as long as their advice is truthful and born from experience and not just dogma they've garnered from other writing experts. One person's truth is, afterall, still truth, even if it's not yours.
But the fact remains - you can't tell between good or bad, relevant or irrelevant advice, until you know enough about writing – or more importantly your writing – to know the difference. And the only way you can do that is to keep writing and to keep making mistakes, because writing experts can't tell you, they can only show you the way. The creative responsibility is yours and yours alone.
But you won't believe me - and you shouldn't - until you've found out the hard way.