I'd already finished my manuscript by the time I picked this up in a second-hand bookshop, so I can't comment on the writing exercises. Nevertheless, it's been invaluable as a guide on how to format my work and submit it to agencies.
The first half of the book covers planning your writing and how to approach it in a professional manner. It covers the markets (fiction, non-fiction and illustration), details like reading age, and how to progress from a first draft to submission and dealing with acceptance or rejection.
This book has an excellent layout (as you'd hope!) - it's very easy to skim through and pick out the topics you need, which are clearly explained yet sufficiently detailed. Best of all, it's peppered with advice from publishers.