Size
Contrast in size is pretty straight forward. You have big type along with little type. The trick to making this effective is to make is obvious. Don't be afraid to use two incredibly different type sizes. If you don't push the difference your design may look more like a mistake(4). You might be thinking that it will attract too much attention but that is the reason why we are doing this. If you are not trying to draw attention then leave all the type the same size (Williams).