1.) You must write.
2.) You must finish what you write.
3.) You must refrain from rewriting, except to editorial order.
4.) You must put the work on the market.
5.) You must keep the work on the market until it is sold.
Keeping Heinlein's rules in mind have helped me get past these roadblocks, though.
1. You must write.
If you have an idea for a book, stop thinking about whether you have the necessary chops to do justice to your idea. Just write. The only way to know how it's going to turn out is to write.
2. You must finish what you write.
There are times when I'd finish one chapter then delete everything and rewrite it again. There are times when I find myself rewriting a chapter over three times in one sitting. THIS IS COUNTERPRODUCTIVE - or at least it was for me. Even if the chapter feels wrong, just go ahead and keep writing. As the story progresses, you'll be able to see the bigger picture. That's the time to ask yourself about that pesky chapter - is it really as shitty as you thought it was? More often than not, I find myself stunned that the chapter I had so much trouble writing wasn't really that bad. It was just my usual insecurities making trouble for me.
And if it is as shitty as you thought? Then you'll likely have a better idea on how to fix it since you've got more of the story written and you know your characters better now.
3. You must refrain from rewriting, except to editorial order.
Of the five, this is the most debatable - the most argued about and understandably so. But there are many ways to interpret it and the way I read it, this is just like Chapter Two but it's more about momentum. If you've found your momentum - DON'T let go of it. Don't let rewriting slow you down. Keep writing - type, type, type until your fingers are sore, your eyelids have started to droop, and your brain's shut down.
Also, waiting for editorial comments is more time-efficient in my experience. As I know I'm both a perfectionist and an insecure writer, my "inner editor" tends to be very opinionated and nitpicky. Because of this, I used to find myself wasting precious time thinking about silly stuff. Now, I avoid all that by waiting for my editor's opinion. If she picks up on the same thing then that means it really is something to consider changing or improving. If she doesn't, I voice my concerns and see what she has to say.
4. You must put the work on the market.
I think this rule applies more to those looking for a traditional publishing deal. You need to keep querying until you find an agent - keep working on your book until your agent scores you a deal.
5. You must keep the work on the market until it is sold.
For indie authors like me, I interpret this rule as continuously working on your book until you start selling copies. Rework your title, your blurb, your sample pages, your cover, your pricing. There are so many ways to improve a book so don't give up on your work too quickly.