I tend to rely on out-of-the-blue inspirations (maybe too much, in all honesty), and my most recent revelation was to look through stock photos until I found my main characters.  This may sound kind of lame, but I really did not have a precise vision of Tess, James, Emma, and Oscar.  I had a good idea of what each character looked like, but seeing the photos really made a big difference for me.

There are quite a few stock photo sites out there, and I went with FotoSearch and 123RF.  It was kind of fun search through the pictures, and it was great when I found the right ones.

Is it necessary to see your main characters?  Am I doing this backwards?