Sorry if this is to late but this is how I do it, every one prolly has a way to do it so maybe this will help you . . .
1. Start with ur hair down; and part a section out about 1.5-2 inches wide by 1 inch. in the front center of ur head. I guess this size would depend on ur head and the results u want.
2. Put the part'd hair in a rubber band or bobby pin. Just to keep it out of the way.
3. Put the rest of your hair in a pony as you would normally. If you have shorter hair or fly aways, you may want to use hair spray. This will help your poof look neat.
4. Take ur hair that u section'd out, of however you were holding it up.
5. Now flip ur head over, like you are looking between ur legs. Brush the parted hair down. Spray hair spray on the hair, careful not to catch ur pony. I dont recommend to much but just enough to get a good hold. Let the hair spray dry a little.
6. Now stand up and comb the hair up, if need be you could add more hair spray now. Grab close to the ends of the hair but not at the ends.
7. Twist the hair 2 or 3 times, bring the hair down to your scalp and push it closer to your forehead until you get the POOF you want.
8. Secure it with a clip, or I find 2 bobby pins placed like an X works very well!
9. If the hair that you cliped has ends long enough you can now take ur pony rubber band out. Holding ur pony in one hand gather the ends in to the pony with the other.
10. Put the rubber band back on like a normal pony and ur set!
*Be careful not to pull the ends when re-do'n the pony or u'll un-poof the poof! *
Whewww so much for such an easy hair style, it's cute tho so ROCK it!