1. Add some heat activated serum onto your hair, or even some anti-frizz serum. These work miracles, you just need to do this before you start drying your hair.
2. You must dry your bangs first, however, if you have a cowlick, it might be pretty hard to get your bangs all the way straight, but that doesn't mean you cannot try. Hell, a little natural wave can look pretty good though. You will need to take a round brush, and brush your bangs down while you point the dryer at your bangs. Please be careful, and keep the dryer at least 6 to 8 inches away, or it might just burn you.
3. Now, if you want volume, just flip your hair upside down, and brush it while you dry. However not everyone wants volume, at least not all the time, then just take sections at a time, and brush it with the round brush, while you dry.
It's pretty much done now, however, you do not want to brush your hair for awhile, if you do, it's going to get frizzy, and you may lose the straightness in the process. Now, keeping this style for as long as possible, such as most of the day, will most likely require you to apply some hairspray.
Now do you see how easy it is to get your hair straightened without resorting to a hair straightener? It is quite easy isn't it? Now you will never have this problem again, you'll be able to switch back and forth from wavy and curly, to straight anytime you want.