My hair used to be pretty straight, save a few baby hairs here and there that would have a slight curl to them. But in recent years, it has gone sort of wavy... which I think I owe to England's humid climate. Click through to see my secret trick if you're looking to get perfectly wavy hair...
I call it the claw. (check out the link to see which one I like) I always use my claw after taking a shower, when my hair is about 70-80% dry, and then I let it dry the full way through before I sleep on it. This gives it the volume that it needs, as well as the curl from twisting it loosely before putting my claw over it.
Voila! I hope this works for you, because I always notice a difference when I use this trick.