Not much to add, the other comments are pretty good. I learned the most from Apple's sample source code, and from reading through open source projects on GitHub. Also, my former company send me to WWDC and the sessions are pretty insightful, too. If you pay for an Apple Developer membership, you get free access to these videos, and many of them are worth it. Though nowadays it's mostly iOS. In 2007 or 2008 there were lots of introductory Mac development presentations.

It's probably best to start with a small project and tackle one project after the other.

I also read this book which helped since it tackled all the basics that one needs to know for a full Mac app. It's german only though (http://www.amazon.de/Objective-C-Cocoa-Nachfolger-Tiger-XCod...) alternatively the aforementioned Hillegas (http://www.amazon.com/Objective-C-Programming-Ranch-Guide-Gu...) which is really good.

'Become an XCoder' free eBook that is a fairly basic introduction to Objective-C and Cocoa programming.

'From C++ to Objective-C' is also good eBook. http://pierre.chachatelier.fr/programmation/fichiers/cpp-obj...

I also bought 'Cocoa Programming for Mac OS X' http://www.amazon.com/Cocoa-Programming-Mac-3rd-Edition/dp/0...

Cocoa is quite different than anything I had programmed before. Once I wrapped my head around nibs, IBOutlets and IBActions it was fairly easy. Once I got going, the apple developer docs were all I needed, but learning I found easier to do from a book than the docs.

There is a ton of documentation and example applications on Apple's developer website. Most major parts of the API have example applications.

https://developer.apple.com/library/mac/navigation/

If you already know how to program then this is a pretty great resource.

There are also some introductory articles to help you get started. For example: https://developer.apple.com/library/mac/#documentation/Gener...

The books by Aaron Hillegass are good. I also like the Cocoa book by David Chisnall.