...any way you like! (But here are some tips....)
In all cases, wear the falls as high on your head as possible (looks more natural). I flip my head over, comb out my hair (as if I were trying to create the "I dream of genie" high ponytail). Then use both falls (at the same time) as if they were a normal ponytail holder and twist them in. Flip back over your head and Viola! You look amazing (or at least more amazing than a few moments ago!)
Here are some faves:
1. The one I just described. ;-)
2. Since I give you two, you can wear them as high pigtails.
3. While in pigtails, take the top half of each and twist into a bun (So you have half in a bun and half down).
4. The same, but with the single ponytail.
5. Braid them.
6. The sky is the limit! Have fun!