Google released a very useful guide called the The Guide To The App Galaxy to teach mobile app developers on how to create successful money-making apps so that you can quit your job and make good money out of it. The cool site is built in HTML5 where you navigate a rocket as it covers 4 main topics and steps in mobile app development which applies to both iPhone, iPad and Android:-
It provides a whole bunch of useful tips but the one I found most valuable is the real case studies from apps like Angry Birds, Ant Smasher and The Weather Channel. It debunks the idea that paid apps make more money than free apps with ads. So check it out if you’re a mobile app developer.