Well over the years i collect cool images that i find from the web, and i stick them into a Inspiration folder. If i'm stuck i browse these images and cook a new creation.

For example the lulu on the walk project, i found a nice anime image of a character (no not Wizard of OZ and for sure not O.Z :p )

Well extualy to be honnist that character had an halloween look, and from that image i got sparked to another idea.

So the only suggestions is watch movies, shorts, images even playing rpg games can trigger your mind into a creative blast! it helps me.

If your stuck, don't forse yourself do something els, even if it's a paying freelance job, don't break your brain, just don't be gone for weeks :p

Also reading interviews, watching concept sketches do the trick!