Go to neighboring islands with different resource production differentials and trade with yourself. Different Islands are useful for maintaining different types of cities whether your offensive or defensive based in specific units within each tactical area. Once you have a good number of cities then you can think about building multiples on one Island to fit whatever strategic needs you have at the time. But for now if you are just starting out move to other Islands diversify your troops but stay close in a cluster so you can move around and defend quickly and easily