Hi there,
It really depends, if you have knowledge in React, then the first thing you should do is to follow the official introduction. Otherwise you should start learning the concepts behind React because the React Native base and concepts came from React.
The way i have introduced myself to React Native was first reading the introduction, setting the environment, after looking for some boirpolate to start a project and then start the project. May be today there is a lot more resources than 4 months ago, and the resources that works for you depends on what you like.
There are some video courses like React Native Fundamentals and Build Cross Platform React Native Apps with Exponent and Redux. The point here is there are so many resources to learn today, but some key concepts you have to dominate are:
And some advices:
Good luck!