When I have design block I usually do things completely unrelated to what I'm trying to do. Usually something I like doing, like listening to music, or going to see a film. If the design is REALLY bugging me then I doodle a bit of things like people, animals, whatever really and then once my brains rested from the original problem I start looking at it again with a fresh brain. Alot of the time I try to do it with instinct and build up from that starting point. However I do make it a habit to have a piece of paper on me and a pen. (If I'm going somewhere I'll bring my special A5 zipped ring binder with compartments) Zipped ring binders are excellent for keeping safe and organising loose and bound bits of paper.