You start off on one side of the coast, with the enemy base on the other coast. Don't waste any time looking for resources on other islands, because apart from a few trees, there is nothing to find. The key to victory is a strong navy, so gather plenty of wood and build a few docks. Once you've sunk their navy, you can send over a few soldiers - Hoplites and Chariot Archers are both quite effective. Find the artifact (located at the back of the enemy base) and finish the mission.