Scoring and Arranging for Brass Band, Andrew Duncan.
 
Andrew has composed this book in a very readable and understandable way. It can be read front to back or by jumping in to the various instruments or topics.
 
The essential reference book for brass band composers and arrangers.
 
It’s a fully illustrated book with many solutions, suggestions and tips on all aspects of scoring and arranging for brass band.  With detailed information on each of the brass band instruments, the different sections and also a focus on the Percussion and Timpani sections.  There is also an introduction to self-publishing and the things to consider concerning copyright law.