I don't bother to wait for inspiration to hit. I write whether I'm inspired or not. It might not all be beautiful, it might not even be on topic. In fact, it might be the worst lines I've ever written, filled with grammar mistakes, poor penmanship, ridiculous prose and complete nonsense, but one word turns into two and that turns into a sentence, then another until I have a paragraph and a page.
I'm never waiting to write perfection. I'm writing because it's what I HAVE to do, like breathing. The more I do it, the easier it becomes to fall right back into the story. A better question would be, how do you STOP writing when you have to?