Most of the islands have at least a small airstrip and TACV operate their inter island flights between all islands except Brava, Santa Antao and Santa Luiza, these are served by boats.
If you fly in with TACV you can book internal flight passes in advance at reduced prices, valid for up to 21 days. Groups can book the Cape Verde Express air taxi service, a bit more expensive but convenient for parties.
Car hire can be a good way of getting around the islands and is available from most larger towns.
Remember in Cape Verde you drive on the right hand side of the road and you will need an international driving licence. Taxis are called Aluguers and that name covers anything from cars to vans and mini buses, fix the price before setting off. The public bus services are cheap and of a surprisingly high standard. Apart from main roads, be prepared for some rough terrain!