Cover and content design are subject to consideration on many levels. I have often been asked to look after production issues, such as sourcing and liasing with print-houses, handle considerations of paper-weight, paper-colour, printing techniques, and other production elements that effect the client's net production costs.
Cover design is an enjoyably creative endevour. It is also very challenging. Design direction is based on many factors, including the marketing direction, whether the book is part of a serialised set, the gendre and tone, the client's budget and printing considerations.
Typesetting and interior book design could be considered a speciality in itself. Typically design and typesetting choices are informed by the target market demographic, the tone and gendre of the content, the number of pages and chapters, any included photos and/or illustrations, and print-production considerations (such as the paper-weight and colour, plus resultant issues, such as dot-gain and the print method to be used). And last, but not least, binding.