Here is a very fast and simple hairstyle that is great when you're short on time. It's called the Knot Braid because it's just a series of knots.
This style works best with long hair because it takes up a lot for each knot. (My princess has hair a couple inches from her waist and you can see how much shorter it is once the braid is done.)
Begin by pulling the hair back into a ponytail. Divide that ponytail into two equal sections and cross them over each other and pull the top section up and through the back and then pull to tighten. *Basically you are doing the first step of tying your shoe - a half knot. Now just repeat the step of creating a half knot over and over again until you run out of hair.
Secure your braid at the bottom with an elastic. It has a very full and chunky look and it pretty cool!