Myself, I "jump tracks" and work on something else for a while -- another story, an essay, a bit of verse, random thoughts, story idea entries, etc. Or I pick up a book I know tends to rejuvenate my excitement about writing, or which tends to teach me more about the craft each time I read it. Often, by doing these things, I find that I not only feel reinvigorated when I go back to the piece I'd stalled on, but in the meantime I've also either begun or completed something else I can be proud of, as well, or (in the case of jotting down story ideas) I have various scenarios playing over in my head as I begin to formulate what to do with these, giving me something fresh and exciting to look forward to....