You can wash your hair and then blow dry it completely or let it air dry and then style after a few hours. Pour a dime-sized amount of mousse into your palm and rub it between your hands for about 5 seconds. Run it through your hair and then use a brush to distribute the product more evenly.  Mousse will give your hair texture and will help set the curls with the curling iron.  Some mousse products contain heat protectants that will prevent the curling iron from damaging your hair. If your mousse doesn't have this, spray a separate heat protectant product on your hair.

Summary:
Start with dry hair.