I've noticed that some of my colleagues are very impressive whiteboard scribblers, being able to do quick-and-dirty flow charts or mind maps that communicate their thoughts and ideas very clearly. Me, on the other hand, often find myself with scribbles that confuse even me. Have you found yourself in a similar situation and actually managed to improve your scribbling?
Show certainty while scribbling. Even if your scribbles look terrible, if people feel like your mind is magic, then no one will care about bad handwriting or whatever.