I wish I knew
Honestly, Picatrix comes from a really weird dream that I had last February. I remember waking up and thinking, 'That would make a great comic idea', so I wrote down what I could remember which was mainly the big plot points (like, up to this point, Winnie being kidnapped and then, the ball).
Where the characters come from really eludes me... with two exceptions. Winnie pretty much acts exactly like I did back in my freshman and sophmore years of college... actually, that's kind of embaressing to admit... heh, oh well. By the bye, Red from the comic Normalness is also based on me from that time... ( http://labrats.keenspace.com/d/20020109.html
Crystal Summer is based on a coworker of mine back in college, who has since, unfortunately, passed away.
Three characters, Winnie, Crystal Spring and Sadie, are all taken from an earlier comic I did, called The Anubis Chronicles. That was really an experimental learning-to-design-comics work and wasn't really any good, so it's not online anymore. I'll probably post some images from it once I unpack (I'm moving in a week and a half)...
Ah, but the guys... there must be a muse hanging over my head, helping me come up with them. Sometimes, their personalities even surprise me, especially Samael...
Hope that was a good answer