In this video I show you guys how to reroll properly in Fate/Grand Order. I provide an overview at the beginning so the meat and potatoes are in the first minute or so. The second part is just to avoid some questions.
This works for both Japanese, and English versions of the game, but since (at the time of upload) English servers are out, and they give a lot of quartz due to the facebook campaign it is easy to do 13-14 rolls.