When I was stuck on something, I'd do something completely mundane - like go soak in the bath or wash the dishes. I often found that a bored mind begins to wander and often, once I wasn't consciously trying to force it to arrive, it would wander in precisely the direction I wanted it to and I'd be reciting dialogue in my head by the time I was done and dashing to the computer to write up my scene shortly thereafter!
LabRat