Personally, I have two ways of overcoming writer's block: either attacking it head on, or letting it simmer for a while.
When I attack it, I grab pencil and paper (for some reason going back to handwritten notes works wonders) and begin to write. It doesn't matter if it makes sense or not. I write about random things. I try to describe the curtains. I imagine a set of curtains in a spaceship. I imagine torn curtains. I wonder who would have torn curtains. In short, I brainstorm for at least twenty minutes. Longer, if necessary.
This is particularly helpful when I sit down to begin each scene, though I usually already have a general idea of what happens, it helps to brainstorm it and flesh it out.
If I've brainstormed and still haven't pushed past the block, I let it simmer. It usually means something is rattling around in my head and I need to let it flesh it out some more. While it simmers, I don't try to write. I take a walk, begin sketching, or relax in some other way. After a day or two, it will usually come to me.