Enable iOS simulator's "Connect hardware keyboard" from menu Hardware > Keyboard menu.

If you are using a non-QWERTY/AZERTY keyboard layout you can use the Hardware > Shake Gesture to bring up the dev menu and click "Refresh"

Something is probably already running on port 8081. You can either kill it or try to change which port the packager is listening to.
$ sudo lsof -n -i4TCP:8081 | grep LISTEN
then
$ kill -9 <cma process id>
Edit AppDelegate.m to use a different port.
Permission settings prevent Watchman from loading. A recent update solves this, get a HEAD install of Watchman if you are experiencing this error.
If in the react-native init <project> phase you saw npm fail with "npm WARN locking Error: EACCES" then try the following: