Developing Character

I admit that I don't spend a lot of time before I start writing a manuscript to outline my plot, sketch my characters, or create an emotional arc.  Instead, I write and let the characters develop themselves and the plot.  

I know that there isn't only one right way to be a writer, but here's some advice that I learned about character development from published authors at the Writing and Illustrating for Young Readers conference:

• All characters--heroes, villains, and secondary/tertiary characters--need to have strengths and weaknesses. (Alane Ferguson)
• As characters matter more to each other, they matter more to the reader. (Brandon Mull)
• Make sure secondary characters aren't "cardboard"--especially parents and young children. (Sara Zarr)
• Avoid stereotypical characters.  Each character must be "fresh." (Alane Ferguson)
• Characters need to relate to others, be interesting, and be likeable. (Brandon Mull)
• Be personally involved.  Be passionate about your characters and connect on deeper levels.  (Sara Zarr)

 What about you?  Is there any other advice about developing characters that you can add, either with your own experience or from conferences you've attended?