The smaller the sections you are writing, the easier it will be to see how they fit into the larger picture. If you are having problems conceptualizing a long fiction story in its entirety, then consider making it two or three stories instead of simply one. It's a common thing to have a book begin with a chapter on one thing, then continue with a second chapter contiaining an entirely new story. This is a wonderful exercise for the imagination, if leaped into, because your creativity will exert itself making stories meet. Writing Backwards Take a look at the outline you've put together.
Chances are, most of the action and conclusion appears in the end of the text.
Many writers find that if they write the ending of a piece first, then proceed to the beginning, there are no loose ends to tie up after writing. Creating backwards is the easiet way to coherent whole. It also eliminates the gaping hole that many writers sense at the end of a manuscript. Creating an end to proceed toward creates a comfortable journey. The shape and content of novels has changed greatly.