Understanding characters and restrictions.
John Passarella, author of both Buffy novel Ghoul Trouble and Angel novel Avatar, explains a little more about outlines and sample chapters. "The outline proves you've thought the plot out from start to finish, and the sample chapter demonstrates you can 'write' the characters."
The Buffy books’ subtly different continuity can also affect the nature of your proposal. "In addition to basic specs, the guidelines impose certain constraints on the aspiring Buffy author," says John. "If memory serves, I started outlining Ghoul Trouble in the summer before the fourth season began. At that time, per the guidelines, I had to write in an 'alternate third season' of the show [without Faith or the Mayor]"
Bear in mind that if you do get commissioned on the basis of your sample chapter, you’ll need to write a whole lot more before you’re done . A typical Angel book requires at least 65,000 words and a Buffy novel around 75,000 words. You’ll almost certainly have to rewrite sections at the request of Lisa, Fox, and possibly even Joss too.
Don’t forget to think big if you want to. Epic special effects have to be used sparingly on a tight TV budget, but cost nothing Buffy Stuff. "One thing you constantly hear about writing media tie-in books versus writing for the television show, is that the author has an unlimited budget since his story exists only on the page as printed words and doesn't need to be produced with actors and sets and special effects," says John Passarella. "We all have unlimited special effects budgets in our mind."