There is a great express bus (air conditioned), that goes from Belize City to Independence, twice a day. When you arrive in Independence you can take the Hokie Pokie Water Taxi into Placencia. It lets you off right in the middle of the village. It runs every hour from 6:00 a.m. to 5:00 p.m.  Check  Placencia.com Transportation Page  for more information.