Hi John,
Can I refer you to pages 42 - 46 of "Home Building and Woodworking in Colonial America" by C. Keith Wilbur (ISBN 1-56440-019-0) where he both describes and illustrates the best way to produce and apply shingles.
Jack Sobon's first book - "Timber Frame Construction" also has a short section on shingle production on pages 162 - 165.
Regards
Ken Hume