Disclaimer: There are two sets of products listed. One that is name brand and tends to be a bit pricier, and another that can be found easier in grocery/drug stores and runs a bit cheaper than the other versions. Each one will work just as well as the other. I've listed both so that you could get what you wanted solely based on your individual preferences.
Check her Polyvore page for a full list of each product both cheaper and more expensive http://www.polyvore.com/ny_premiere_runaways/set?id=17234735
First comb through, or brush, your hair to rid it of tangles.
Then shampoo and condition hair.
Tip: Shampoo your hair first thing when you shower/bathe. You don't have to repeat. Then when conditioning make sure to apply more creme at the end of your hair, and a lesser amount at the roots. Let the conditioner sit on your hair for a few minutes. The steam in the shower helps your hair to absorb more of the conditioner, thereby giving its ingredients more time to soak in and do what they're supposed to do. Comb your fingers through to hair a few times after applying conditioner to make sure that it is distributed through all of your strands.
Also, rinsing your hair in cold water will help to make it shinier as well.
Step 1: Towel dry/blot your hair dry with a towel. Don't twist it in the towel, as that can lead to breakage. I've clipped a great hair towel on to the Polyvore set so that you can see an example.
Once hair is rid of a much excess water as possible, section off pieces, and spray the volumizing spray directly on to the roots only. I suggested using the spray as it will put the product directly where it is needed the most, and you won't end up with an excess amount that could end up weighing your hair down. Plus, it's easier to manipulate than mousse.
Rub your fingertips all over your scalp to make sure the product distributes throughout your scalp and roots as much as possible.
Next, take the hair creme and rub into your fingers. Then run your fingers throughout your hair starting just below your roots to throughout the ends. Using a wide toothed comb, comb through the part of the hair that you just applied the creme to, so that it's spread evenly.
Tip: If you have short hair to medium length hair, like Kristen, then use only a dime sized amount of creme. If longer than use a nickel to quarter sized amount.
Step 2: Using a paddle brush (so that it gets your hair straighter), blow dry your hair by raking the bristles through your roots, holding the hot air there for about 5 seconds, then lightly pull the brush down through towards the end, and making sure to follow with the nozzle of the dryer as you go.
Tip: This is easier to do if you have pre-sectioned off you hair, and you go piece by piece; or you can flip your head over and dry it upside down.
Once done, use the cool shot to set your hair, and to get rid of any excess frizzing.
Step 3: Once hair is dry, section off a back portion, about 1 to 2 inches worth, of your hair at the crown of your head. Using a fine toothed comb, or the pick end of it, and gently tease the roots only on the underside of the sectioned off piece. Then lay it down so that it blends back into your hair.
Then cordon off another, 1 to 2 inches deep, section of hair from temple to temple. Keep this section separated.
Tip: If you've got long bangs then use those. If you don't have a much as they made for Kristen then you can gather more, or less depending on your preference. If you have short bangs then make sure to grab longer sections of hair behind it so that it can be blended in.
Step 4: Create a French twist by loosely gathering your hair, excluding the front section, at the nape of you neck. Then start to twist. As the twist gets tighter start to pull the ends only up towards the crown of your head. Your hair should start folding over itself to create the twist. Once it won't twist any further, tuck the left over ends into the top of the twist so that they aren't visible. Secure with bobby pins throughout the twist.
Tip: This is easier done by placing a finger in between the prongs of the pin and then pushing the ends through so that it grabs more hair.
Also, feel free to use a lot of them, so that it's more secure, as too much - in this case - is better than not enough. I've found that with thicker types of hair, more bobby pins should be used because it can fall out easier.
If you have light hair you might want to get pins that are colored to match, as on a really light blonde person dark pins would stand out.
Then where you had previously teased your hair at the crown, rub and pull slightly to release some of the hold of the twist to create the volume on the crown of your head. Don't pull so strong that your hair falls down.
Spray with hair spray, and then lightly pat your hair down, while the hair spray is still wet, to flatten any wayward strands/flyaways.
Step 5: Going back to the sectioned off piece, we're going to use a 1.5" wide barreled curling iron. Start at the roots, under your hair - so that the barrel is in between your forehead and your hair (be careful to not get it too close and burn yourself). Then, without using the clamp, wrap the section of hair around the barrel over and over until all of it is wrapped. Then start to pull the barrel downwards through your strands, making sure to keep a slight hold on your ends as you do this process, until it's gone all the way through from root to tip.
Tip: You may want to split the section into two pieces. This really depends on how wide your head is. If you find that you don't get the results you wanted on the first go, then start over again by sectioning it off in to pieces and repeating the steps.
Once this is done, let the hair fall, and then cool down before you touch it again. Once cooled brush through it so that it creates a slight wave. Pull hair up, and spray hair spray directly at the roots so that it gets volume and will stay throughout the night. Rake the section of hair over to one side, and voila! You've now got a wavy bang to go with your French twist, and your own version of Kristen's hairstyle.
Tip: If your bangs are longer than Kristen's, then, feel free to place the excess behind you ear and secure it down with a couple of criss-crossed bobby pins.
Spray a light dusting of hair spray all over again, and you're done. Enjoy!