My MacBook Pro seems to loose WiFi connection after coming back from sleep. Here is what I tried:

1. Go into Network Preferences
2. Turn off Wi-Fi
3. Delete the Wi-Fi service
4. Delete the Automatic location
5. Using the + button to create Wi-Fi again, and then rejoin the network. Also, under the settings gear icon, choosing Set Service Order and moving Wi-Fi upwards.

If this does not work, I will post my next attempt or solution