A simple clown face is an relatively easy and fast design to paint, if you stick to the basic, key elements. Whether or not you paint the whole face a color – traditionally white for a clown – before you start creating a face is up to you and how much time you have. If you're at a party, it'll help speed up your 'production line' to have an assistant who can do the 'under layer'.
So, where to start? Think of a clown and what do you think of first? A bright, prominent nose. But don’t limit yourself to red; using other colors for the nose will immediately make the faces you’ve painted different.