All bus routes can be found here:
http://www.atp.com.mt/atp/servlet/ControllerServlet?action=listWinterBusRoutes
Most important / popular bus routes are:
1, 2, 3,4 & 6 – Valletta to the Three Cities and v.v.
8 – Valletta to Airport (through Tarxien Temples) and v.v
27 – Valletta to Marsaxlokk (M’Xlokk in short, a quaint fishing village) and v.v.
38 – Valletta to Hagar Qim and Mnajdra Temples and v.v
45 – Valletta to Cirkewwa (for Gozo Ferry service) and v.v.
49, 58 & 59, 159, 449 (fastest route) - Valletta to Qawra & Bugibba and v.v.
62, 63, 64, 67, 68 – Valletta to Sliema (some upto St. Julians/Paceville) and v.v
80 – Valletta to Mdina and v.v.
Other routes not using Valletta Terminus
48 – Bugibba/Qawra to Cirkewwa (Gozo Ferry Service) and v.v.
65 – Sliema Ferries to Ta’ Qali Crafts Village & Mdina and v.v.
70 – Sliema Ferries to Bugibba/Qawra and c.c.
86 – Bugibba/Qawra to Ta’ Qali Crafts Village & Mdina and v.v.
627 – Bugibba/Qawra to Sliema Ferries to Marsaxlokk and v.v.
645 – Sliema Ferries to Cirkewwa (Gozo Ferry Service) and v.v.
Check the website above for more routes.
Tickets can be bought from the bus driver and the basic fare is €0.47. Some routes are slightly higher in price – this image shows the different prices: http://www.atp.com.mt/atp/UserFiles/Image/fares.bmp
Always ensure that the bus driver gives you a ticket (which also serves as your receipt for payment). Try to pay your bus fare using small change, preferably coins.