Writing a book is like going on a trip where you get to plot the course, who goes with you, what they encounter along the way, and you get to determine these characters' final destination. Have at least a basic goal, or conclusion to the story in mind when you start writing your novel.
Some authors do an outline to guide them to their final ending. Others claim they play it by ear and write the story as they go. The truth is, all authors must have an idea of what they want to write before they can begin, some just keep that idea in their head, and some write it on paper.
If you are the write-it-on-paper author, don't fill in every detail. A skeleton will do. That will give you freedom to flesh out the story as you write.
If you're the type to keep the story in your head, you will still need to work out directions or at least program them into your mental GPS, so you don't get lost and bring the reader along with you.
Know your story direction and have a plan to get there that works for you. Otherwise, how will you know when you've arrived at your destination?