To reach Ibo independently you will have to get a chapa ride from Pemba (or even more demandingly by changing rides on the rough road from Macomia), from where you will reach Quissanga. From there it is a short ride down to the ocean at Tandanhangue. Usually the chapa runs to meet the high tide and an unforgettable dhow ride to Ibo Island. Be aware that other islands are served from the same departure point. If you do get stuck - perhaps at the low spring tides - there is a shelter to sleep overnight, or perhaps you will find a bed in the village itself.
Any trip on a dhow is rewarding, but approaching the dilapidated fortifications of Ibo is especially memorable. The price locals pay for the one-way trip is NMT 40.