What is the best way to get mud off a horses face?

I use a curry comb carefully on the cheeks, and a dandy for the rest. But it still doesn't all come off! My horse is quite good at first, but after a while she gets a bit ratty about it. I know she needs to be clean before the bridle goes on. How can I make it quicker, easier and more painless for both of us? Any tips?