The usual way it works for me is packing in enough information about the problem, the context, and relevant background/theory as I possibly can - to the point of obsession. Then once I've established a constant background hum of thought, I have to encourage the epiphany to arrive.

Monotonous physical movement is an epiphany trigger. Activities like running, washing dishes, and showering all set the stage for the epiphany to arrive. It can take a week or two when it comes. If it doesn't then I take a break for a month and try again.