It's always good before starting do design for any Apple product to have a quick look at their Human Interface Guideline (HIG) https://developer.apple.com/library/ios/documentation/userex....

They have HIG for almost everything.

I also read that a lot of apps are developed on iOS first http://www.businessinsider.com.au/app-design-company-directo.... I wonder if there's any truth to that.

But saying that I know that Google is pressing their Material Design http://www.google.com/design/spec/material-design/introducti... quite hard lately. Would really love to hear what Android devs think of the Material Design. Are they going to port their current app design to it?