I ran into a blog with comments from a lot of famous writers on this subject the other day. I'd point you toward it IF I could remember where I saw it!
But I thought it was an interesting topic and thought I'd throw in my own experience--not that I'm a famous writer, but I can hope. I've received some great advice from some very experienced authors, but truthfully the best advice I ever got was published and is available to every writer out there. It was Heinlein's famous "Five Rules," originally published in his essay that appeared in "Of Worlds Beyond: The Science of Science Fiction Writing."
They are pretty simple:
Rule One: You Must Write
Pretty simple -- but, amazingly, many people who claim to be authors don't write.
Rule Two: Finish What Your Start
Here it really gets tough. Maybe you think the first pages are weak or the characterization isn't that good. It's easy to give up, but if you don't finish then you don't grow. Half finished stories don't do a thing for you.
Rule Three: You Must Refrain From Rewriting, Except to Editorial Order
Now this one gives people fits. Almost everyone modifies it since none of my first drafts come out ready for an editor to read and I doubt that yours do either. But the fact is, beyond a limited point, editing and re-writing is a lost cause.
Let me ask you this: Do you really know what will improve your work? Do your first readers or your critique group really know? Sure. Fix plot holes and obvious errors. But once you have that piece finished, the plot holes filled in, and reading reasonably smoothly -- STOP! Don't work on it for years. (Sadly, I know writers who do.) You're as likely to make it worse as you are to make it better, unless you deliberately wrote it poorly, and I don't believe that.
Instead of working and sweating over that piece, try to make your NEXT one better than the last.
Rule Four: You Must Put Your Story on the Market
Obvious, but most of us fall down on the job here. I admit it. I have a couple of stories I need to get out. Sometimes rejections or even the fear that you will get a reject makes you stop. So reward yourself -- have a piece of candy or whatever works, but get that work in front of editors who can buy it.
Rule Five: You Must Keep it on the Market until it has Sold
Tough! Tough! Five rejections. Ten rejections. You start thinking that the piece must be crap and you should trunk it. But keep putting it out there. I don't think Heinlein's remark that there is a publisher somewhere who is "so desperate that he'll buy the worst old dog you or I or anyone put out" is true any more. But I do know authors who have sold stories on the 70th submission. So just keep trying.
So that's the best advice I ever received and to be honest just about the only writing advice (besides Stephen King's in On Writing and a couple of other books I mention on my website) that I ever bother to follow.