I remember that Livia Blackburne once explained in an interview that there are two paths of thinking, the deliberate path and I think the spontaneous path. The deliberate path is when you focus your mind on something (i.e. sitting in front of the blank page) and the spontaneous is when you don’t focus on anything specific (i.e. performing an automated skill like showering).
In the same manner, there are also two approaches to thinking called convergent and divergent thinking (whether there is a link with the paths, I don’t know, but probably).
Convergent thinking limits options, i.e. taking available options and whittling them down to one. E.g. Choosing a colour for a wall from a catalogue. You cut out any colours you don’t want until you find one that you do. All your thoughts converge on one location.
Divergent thinking expands options. E.g. Choosing what to do with your wall. You churn out the maximum number of possibilities. All your thoughts move away from one location (you could paint it, or draw on it, or plaster it with pages from the Lord of the Rings).
As you might have guessed, creativity is divergent thinking. Thinking outside the box. Though the convergent path is important in some instances, thinking of a story is not one of them.
It is very easy to fall into convergent thinking. The problem is that you are only using available ideas instead of creating new ones. To be a divergent thinker, you must put your mind to it.
However, there are a lot of times when we get stuck in convergent thinking (which is possibly one of the causes of the so called “writer’s block”). If you’re in there, try branching out.
By branching out, I mean change your medium. Write poetry (like a lot of novelists do). Change from novel to short story for one tale. Paint. Write the storyboard for an indie RPG. Knit. Whittle wood.
Branching out forces your perspective to shift and your mind to start thinking divergently (because you have no or little ideas to limit).
Paint, even if you can’t.