Defaulting my WiFi connection
Go to System Preferences -> Network.

On the left sidebar click Wi-Fi and then "Advanced" at the right bottom corner.

Now choose the tab Wi-Fi and you'll see a list of all the wireless network you joined. Drag networks in the order you prefer (e.g. the domestic network should be the first).

Update: on the same screen, if you want to remove some of the networks your computer has joined simply select the network name and then click on the - (minus) button to remove it (Note: your computer will not join automatically that network again). If you want to stop listing networks, on the same screen, uncheck the option "Remember networks this computer has joined"