Visualizing 'visually' with my eyes closed is extremely difficult for me, but I find that if I can introduce the other senses with my 'imaginary' body first, sight comes far more easily.
I use
Erin's 'go to your room' meditation at lot. The room at the top of my elevator happens to have a deep shag carpet, and I refuse to let myself even try to look at the walls, the elevator doors, or at anything else until I can 'feel' the carpet there. I touch the walls, then, noting the texture of the paint, and allow myself to look at simple colors and objects. I progress from there.
It might not be applicable to all sorts of visualization and might not be quite orthodox (hey, though, it's my head), but it has certainly helped me.