The way I do it is when I finish more of the skeleton of the application, then I try to find a PB that matches the image in my head.
Illy went through a couple PBs, I can't remember off the top of my head who else. But I kept circling back to Kaya that I went, "fuck it. let's go with it." The problem I was having was to either do a Real Life 18 (which Kaya is) or a Hollywood 18 (a 20+ actress playing an 18 year old. Hay every CW show ever).
Nicky didn't go through any other PBs that much, cause I went through an icon directory and they had his floppy bangs and bashful face. And I went "Hey you're Nicky!" I almost didn't want to use him cause of lol Stonems -- Kaya and Nick played siblings. But in the end, I just liked him best.
Devin was easy, cause I loved her god damn face so much.
And Wishbone (and PBS) was the only thing my gramma would let me watch at her house. It was awesome. I want that dog.