You now have all the tools you need to design, build, and launch apps for iPhone, iPod touch, and iPad. As with any other endeavor, there is always more to learn. There are also many kinds of helpful resources, including books, websites, developer groups and conferences, and social media.
This book is just one in a series of iOS hands-on books. Your app might require you to have a deeper understanding of particular topics. Look for these other books in this series:
Learning Objective-C 2.0: A Hands-on Guide to Objective-C for Mac and iOS Developers, second edition, by Robert Clair
Learning iOS Design: A Hands-on Guide for Programmers ...