Here is what you do:
Set someone to do a quickening. Look at the names at the bottom of the screen that should have a Square, Triangle or X accompanying them. If there are names, press one of the three above buttons (the one next to the name that is up). That will make a second person do a quickening after the first one is done. During the second person's quickening, do the same thing and keep going.
If you have no names, press R1, which will like scramble up the names, and then maybe some names will pop up. If not, keep doing R1 until they do pop up.
In addition to name popping up, a MistCharge will pop up as well. When those pop up, it would be a good idea to click them, as it is guarenteed that after you press that (and after it scrambles the name again) the person whom you MistCharged should be ready to smack the enemy with another one of their quickenings.
^^;; At least, that is how I can explain it, I'm not very good at expaining unfortunately. I think if you look on gamefaqs.com or something someone might explain better than me.