I learned to machine applique from Harriet Hargrave's book on the subject. Here is a link to the current edition of her book:
http://www.amazon.com/Mastering-Mach...dp/157120136X/
She covers multiple methods and provides a *lot* of very helpful tips for getting started. Lots of great photos too, at least in my older edition of the book. I think parts of this book may be available for viewing online; ran across it sometime last year.