Since I didn't liked to learn from video courses, I mainly focused on tutorials that provide built-in editors and blogs.
You should be aware of some mostly used ES6 features like arrow functions, classes, destructuring, const and let keywords, Promise, template strings, module imports, rest and spread operators. You can learn about them here
Once you understand them, start learning ReactJs. You can get started from the official website as it is well documented and has a tutorial to build an app. Use your ES6 features here to get used to it.
React Native uses Flexbox layout style to render views in a much easier and responsive way. I felt a bit difficult to understand the concepts of Flexbox, but I recommend reading this guide to know all about it. You can keep it open in a separate browser tab so that you can go and refer it whenever you face any difficulties.
If you clearly understand all the above concepts, then it'll be very easy to learn React Native.
Also choose an editor of your choice to code. I personally prefer Visual Studio Code. It has some great features and a whole lot of extensions to make it easy to code.
Now you are ready to learn React Native. Go to their official website and go through their getting started guide to build a sample app. Read all the basics provided in the docs.
Once you get an idea of how to build an app, start doing a demo app to apply all the features you learnt. I started with a Todo app. Avoid using any libraries at first. Try to use what you learnt so far to build a basic app or atleast complete a few screens. Once you complete that, learn to use libraries.
While choosing libraries, always decide on the ones that are well maintained and recommended by the official docs.
Since an important function in mobile app is how to navigate between screens, it is important to know how it's done in React Native. As of this writing, RN recommends to use libraries like ReactNavigation and React Native Navigation to use same code for both Android and iOS.
Go through their docs and apply the library in your demo app.
Finally learn how to build a Release version of your app.
That's it. If you came up to this stage, then you are ready to build a production ready app.
If you are a iOS/Android developer and learnt React Native, share how you learnt React Native as comments below.