This is totally new so I don't think anybody has reviewed it yet... but:

Facebook's own tutorial is quite good I think (caveat: I wrote some parts of it), so I would definitely recommend going through that first. It's a really great overview of most React Native concepts.

This gives more in-depth and hands-on instructions. E.g. creating a project from scratch and building it to completion, one step at a time.

reactnative.com is an aggregator of useful topics, news, and links (a few of which are tutorials), so it's a bit different, but also very useful when getting started.