How many days should you plan?
With one day, choose between exploring the town on foot and a day on the water. With two days, do Stone Town on the first and Changuu and Nakupenda on the second. Leave some slack in your schedule, because times at sea depend on the tide.
Where should you stay?
From Stone Town you are close to the harbour for trips to Changuu. Nungwi and Kendwa, in the north, are handy for booking a boat trip to Mnemba. On the south-east coast, check the tide before you fix a swimming slot.
Watching dolphins from a distance
Before you book, ask how the boat behaves around the animals. Let the dolphins choose their own distance, and skip getting in the water if several boats are crowding around them.