Unasked for advice.

Obviously, I'm running into lots of writers, and almost all of them say the same thing.

"I started a book.

 Or "I finished a book and need to rewrite it."

 Or "I have a good idea for a book."

So, I want to give them unasked for advice.

Finish the book!

Make a deadline and stick to it!

You aren't going to be perfect no matter what you do, so you may as well finish the book and learn your lessons and go on.