It is nice to use samples in published authors' books but I have found it more effective if I read good introductions that have been written by the students. Another thing you can do is teach some of the "good beginning" concepts and then ask permission to use one of the student's pieces of writing with the idea that the rest of the class is going to create a new beginning. Let the kids help their fellow author with ideas. You will be amazed at how their beginnings will be even more impressive than well-known author's beginnings. It will be more meaningful and exciting when teaching each other instead of learning from "the best."