Can't connect to Wi-Fi

Make sure Wi-Fi is switched on, and the device isn't in flight mode.
Check you've picked the right network: guest and staff networks are often separate.
Forget the network and reconnect, re-entering the password carefully. This helps if the password has changed.
Restart the device.
Move closer to the access point: thick walls and metal get in the way.
If other people can't connect either, it's probably the network rather than your device. Tell us how many people are affected.