I would work on building your foundation knowledge of iOS through books such as iOS Programming by Big Nerd Ranch and Cocoa Programming by Big Nerd Ranch. I would go through the Cocoa book first since many of the concepts for iOS were developed from Cocoa under Mac OS X. This way you will see some of the evolution of iOS. I have read these and a handful of other iOS / Cocoa books. These two books are the best of what I've seen.
I suspect that many people have difficulty understanding the Apple documentation. Hopefully you won't fall into this category (but I do). My opinion is that Apple documentation is written for well experienced programmers. Don't feel bad if you have trouble with it.
Instructor-led training is pretty expensive. I've not done this yet but it would be helpful. The advantages are obvious: someone experienced there to help you, and immersion in iOS programming for some number of days. Compare this to pecking away at some iOS book for a few hours per day with no help. This is one of the less expensive training classes I have seen: http://iphonebootcampnyc.com/iphonetraining/
