The first thing you should do when you arrive at your destination in Malta is to buy a 7 day bus ticket, this will cost you €6:50 (all prices at February 2015). This allows the ticket holder to hop on and off and use as many buses on as many routes as one can squeeze into the week for which it is valid. It is excellent value and the buses are scheduled to run about every 30 minutes, although this can be up to an hour on some remote destinations from Valletta. The bus station at Valletta serves every corner of the island and is the main bus hub.         

Arriving at the airport the X numbered buses serve very many parts of the island even the ferry to Gozo.

On the subject of the Gozo ferry, the ticket is purchased on the return journey from Mgarr on Gozo, so don't panic if you step aboard the ferry ticketless from Cirkewwa ferry terminal, and what's more it is only €4.65 return, though you've already made one journey. Also a day ticket to hop on and off on Gozo is a budget busting €1.50!!!

There has to be a downside and it is that you may end up waiting for a bus that doesn't appear at the scheduled time. Small price to pay for such incredible value.