I know I know… Books are played out. But Ive learned a lot from the books listed below about orchestration in general.
Principles of Orchestration, Rimsky Korsakov- This is basically a one stop shop for all things orchestration. It has examples from his own works that really help with identifying subtle things you can do to change the all around timbre of your composition. I learned a lot about woodwind composition from this book.
Orchestral Technique, Gordon Jacob- This is a pretty nice book too. Its very comprehensive, and really good for reference later on. The exercises at the end of each chapter lead the reader from gradual stages of writing to more complex levels later on.