I’ve talked about this before, but I really need to beat it into my brain so I don’t make the same mistakes again: I cannot separate plot from character, character is plot and they decide what happens. Granted, it’s good to have a general idea what’s going on, but I imagine that is just you pointing down a road that leads to where you want your characters to go. They are the ones deciding, however, if they’ll take a short cut, go back, take a rest; or move in a different direction entirely.
You are forbidden to help them and show the way.
So how do you make this happen in practise? Well, in my latest draft, I did it all wrong. I wrote very sparsely on purpose, meaning I left out a lot of things to add later because I was afraid I’d have to change things later anyway. But ironically, it’s only when I neglect to add things as they come that I end up having to change. No writer knows their characters from the get go. You learn about them as you write, which means you’ll have to put them in situations that force them to act and not have a predetermined result for them because then the characters are blank.
I suppose one could do a character sheet beforehand but who wants to do that? It’s boring and your characters will end up bland anyway.
To keep yourself entrained is a good rule of thumb. If the story becomes dull it’s you that have made the choices for them, you already know what will happen. And if you are bored, the readers are bored.