Johnston, Edward. Writing and Illuminating and Lettering, Hogg, London 1906, later editions Pitman now A & C Black. Pioneering handbook on Calligraphy and Handlettering. It's wide ranging treatment defined the field of studies for much of the twentieth century. Some techniques have been superceeded by later developments. This book's real value lies in it's approach to the subject explaining letter-design in terms of making rather than abstract theory.
Hufton, Susan. Calligraphy: Step-by-Step, Weidenfeld and Nicholson, London 1995. This is the book I would recommend most beginners to start with.