I only use really 2 design patterns when working with games in flash the Singleton and Model View Controller patterns. You should look into the Gang Of Four - Design Patterns, I remember reading a book by Colin Mook (cant remember what its called) about design patterns in flash some time ago. All in AS2.0 but would be the same. I think they help you stay in structure but sometimes can make it hard to do really what you want because you have to stick to the patterns rules.