I've spent several pleasant hours with Tom Rudderham's interactive book Photos. It contains a wealth of information about using your camera to the fullest, including those in Apple's iOS devices.
The book contains videos and interactive graphics to make learning all that much faster. Rudderham shares tips and hundreds of high-quality photographs you won't believe were taken on iPhones and iPads.
Rudderham unravels what may be mysteries to many users, like getting photos out of and onto your iDevice, and he has written the best explanation I've seen of Apple's Photo Stream service.
Rudderham explores the iPhone, iPad, and apps like iPhoto, as well as features like HDR, slow-motion, and basic editing. He also describes his favorite third-party imaging apps like VSCO Cam and Snapseed in detail. There's also a good deal of information on Camera+.
The book also includes interviews with 2012's iPhone Photographer of the Year, Holly Wesley and profile of photographer Kevin Russ. There's also an interview with iPhone photographer Kaisa Breeden. I think the most valuable parts of the interviews are the 'what not to do' suggestions from these pros.
I can't think of a better introduction to iOS photography. If you think you already know a lot about iOS photography, you'll be pleased at how much you learn. As you go through the book you'll be constantly wondering if the spectacular photos were really taken with iPhones and iPads. They were, and you'll get a wealth of information and good ideas that will inspire you to become a better iOS photographer.
Photos is available through the iBookstore at US$8.99. It's well worth it, and if I could only buy one guide to iOS photography, this would be the book.
Remember to grab this not in the Apple app store, but through the iBook Store.