There are two types of design within book design:
Book jacket design and interior book design.
Most people want to be book jacket designers (surprisingly, the job didn't exist until the 1900s). It's more glamourous compared to interior book designers.
However, interior book designers play just as crucial of a role to successful book design.
Interior book design is more than just plugging things into InDesign. It takes a lot of studying and work to hone the designer's aesthetic sensibilities.
There are different genres of publishing which each have their own type of design:
Trade and Commercial
Fiction and non-fiction aimed at a general audience.
Professional
Caters its products to the needs of specific professional groups.
Textbook
Educational books for school or coursework.
Within these basic categories publishers might specialise in areas like pop fiction, DIY books, etc.
The largest publishing genre is the mass-market, cheaply produced paperback novels (romance, sci fi, Westerns, etc.) The books you see that are sold in airports, supermarkets, drug stores, etc.
The approaches to graphic design used by different publishing houses are as different as the books they produce. Some follow traditional paths, others are more inventive. It just depends on the publisher.
If you're seeking a job from, or in a publishing house, it's good to have the knowledge of their method (or lack thereof) in order to better suit your portfolio.
Another sector in publishers: book packaging!
These are independent producers who do, and sell, the whole book design she-bang:
Text, illustration, design, and sometimes printed books which they end up selling to publishers and distributors.
Book publishing is a product-oriented industry.
Book jackets play a crucial role in winning a consumer over to purchase the book.
However, sometimes the most original book jacket designs are deemed unsalable by marketing.
"This is an industry of negotiation, compromise, and working with others..." -John Gall
With that quote he makes a great point about how book design isn't just about the designer and what they want, but it's kind of a dance with marketers and how to create something that will be a profit.
Rita Marshall was interviewed about children's book design and mentioned that in kid's books the type, along with the art and words, is an important component to good children's book design.
