Get a 3-day bus pass. It will allow you unlimited access to the buses and the ferries. You can take a high speed Ferry to St. George's and see the entire'Island' on your way back.
You have to go to horshoe beach and you should really have a rum swizzle at the Swizzle Inn.
The bus drivers are very friendly and you can get on and off the buses any where along the way.
I would get a book on the island and find the places that interest you. Bermuda is a great port because you get to spend some time there, so you can see most everything you set out to see.