To run your app , it better to follow the official documentation on this and if you have any problem see below for possible causes

Click here https://facebook.github.io/react-native/docs/running-on-device

Issues

Unable to run on iOS

This probably cause by framework paths and search header paths , which come from facebook , google or twitter sdk, see my XCode configurations for this , you will need to download facebook sdk and twitter sdk and place the path in the framework search path as you seen below