Walk away. Do the laundry. Go to PetSmart. Take the dog for a walk. Call my brother. Take a shower. For some reason, inspiration always hits me in the shower, when I have no pencil or paper handy. Maybe it's the whole "cleansing" thing, that also cleanses the mind of all the BS that's in there jabbering at me - but whatever it is, it works!
Writer's block is like insomnia - the longer you lie there, fretting about not getting any sleep, the worse it's going to get. So after a half hour of this, I get up and go work on something - my Etsy shop or writing or marketing my book - for a half hour, and then I'm sleepy. Writer's block works the same way - you have to take your mind off of it for it to come back.