Wash your hair and then make your hair into small braids. After braiding each portion of the hair, spray it with hairspray. Then go to bed with the braids remaining in your hair untouched. Then in the morning, undo the braids and you'll have beautiful wavy/curly hair! Note: works better with thin though.
You can always wet your hair and braid it and in the morning when you take the braid out, your hair will be wavy. Or, you can always just use rollers! There are some that are very soft and spongey, and you can sleep in them; they make very tight, bouncy curls.
Do a really, really tight, sturdy French braid in your hair. I like to spray it with a little hairspray. Leave it over night. Undo it the next morning, and it will be nice and curly. However, this works better on thinner hair, and your hair will be more on the wavy side rather than wavy.