If you want to get around Sal or any of the other islands in the archipel, take a ride on one of the shared taxis. They're not only dirt cheap, but a nice way to get around and meet local people at the same time.
well... as you can easily guess... by plane :)
You have regular flights there from several origins, for instance from Portugal we had the choice beteween TAP and TACV
you can easily rent a 4x4 vehicle at any of the local hotels