For me, a combination of books and building a real, substantive app works best. I was actually in the same boat as you a couple of months ago. I have significant experience with Ruby/Node, and studied C++/Java in school. I decided to tackle learning Objective-C/iOS from scratch, and it only took a month of part time work to get to a point where I could build some pretty cool things. I documented that process from day 1, when I received the books:

https://giveit100.com/@marbemac/9r2pkz