Have you ever experienced that terrible moment when the free flowing creative juice turns suddenly from marsala to molasses, and the next paragraph gets stuck inside your head, refusing to see the light of day?
Where do you go from here? If you're at this point sadly, it's already too late, as you have begun your long journey without a map, and are now lost in the wilderness.
Writer's Block should never happen, and will never happen, if you begin your project properly.
When you first catch the idea for a book, get yourself a notebook, or if you're writing directly onto the digital screen, write out the entire story in one paragraph. Something like this...

"John comes home to find his wife murdered..the police think he did it, he escapes from them and goes on the run, he has to prove his innocence and unmask the real killer, but how?"

This then becomes the launchpad for the chapters. Begin a new file/page for each chapter and enter one paragraph detailing what happens in each chapter.
C1. John comes home to find his wife murdered.
C2. The police arrive at the house and arrest John.
C3. John escapes custody.
C4. John contacts his old friends. etc.

Notice how brief and devoid of detail everything is at this point, details and creativity will all come later, they are not required right now. Continue until you have the whole story in note form from beginning to end, you know what happens in every chapter and how it all resolves.
Now, and only now are you ready to begin writing. So where does Writer's Block come in? If you use this method it doesn't. You have a map for your journey, it will show you the route from where you are now to where you wish to end up, and all you have to do is follow the road.
No matter where you are in the story, you will always know what comes next, and therefore Writer's Block becomes a thing that only happens to less prepared authors.