I have found that it helps to give the characters an easy subject of interaction. On my last trip, I wore a hat with Disney villains on it, and I had my Magic Band in one of the new Magic Keepers on a lanyard around my neck. Many of the characters commented on or gestured to these. Some of them indicated that they were disappointed that the Magic Keepers look like Minnie or Mickey but not like them! The more interaction, the more photos.
I don't recall if this made a difference at the Disney Visa photo shoot this year. I went late afternoon, and there was nobody ahead of me or behind me. In the past, at that shoot, Mickey pointed to the different illustrations on my nephew's shirt on one trip, and tried to get me to explain the insignia on my hat on another trip.
It doesn't work 100% of the time. Moana knew what she was going to say, she said it, and she appeared really bored by the whole process. Her interaction was not personalized at all. (That was not a Visa shoot, and she's not there any more.)
