Itaparica can be reached in about 1 hour by ferry from Salvador. The smaller passenger-ferry departs from near the Mercado Modelo, while the larger car-ferry goes from about 2 km north of there to Bom Despacho on the main island.
Vans - The cheapest way to get around on the island is by van. There are regular routes all over the island. Make sure you are on the right side of the street and you can flag one down.
Taxi - If flagging down a crowded van isn't your style, you can take a taxi. They are a lot more expensive but are easier and faster.
Private Car - When you arrive in Itaparica, you will likely get approached by someone trying to get you to take a tour by private car. You can negotiate a price and they can take you to all the tourist attractions on the island. They are private cars so be careful whose car you get into.