“Write with the door closed, rewrite with the door open.”
~ Stephen King
On Writing

Mr. King said in his book On Writing that writing is a lonely job–something I more than agree with.  But ya know what?  It needs to be at first, I think.
When you sit down to write the first draft of a book, every opinion of anyone who might read it shouldn’t so much as enter your mind.  Get the words down and worry about how good they might be later–that’s what revision is for, after all.  Focus on the story you’re working so hard to tell.
Closing the door will also help to keep out distractions.  It’s all too easy to get distracted when writing now when the majority of us do it on the computer, where something less difficult is just a few clicks away.  If it takes so much effort, don’t only close the door, but lock it and barricade yourself inside.  If you find yourself too distracted writing on the computer…paper is always an option!  I actually preferred that method for quite a while, but once I get writing it’s too hard to keep up with my brain at that point.  I am even the proud owner of a handful of typewriters; unfortunately, they’re all quite loud, or I might be tempted to use them more often!

Rewriting is a tough process–kill your darlings, kill your darlings….  At the same time, though, it’s very liberating to cut out all of the unnecessary things.  Strip the novel down to the story at its core–it’s exciting to learn more about it along the way.
It’s only when rewriting that you should let a few people take a peek at your diamond-in-the-rough of a novel.  And I say a few because, much as you might want to throw it at anyone who looks in your direction, that isn’t wise.  Pick a few people that you trust and give it to them, first and foremost.

Do what’s necessary to get your story written and enjoy every step of the process!  It’s not for the faint of heart…but it’s more than worthwhile!