First when in Tool research the small wall and put the wall on the very edge of the island. Put 5 villagers or more on this. Upgrade to Bronze. Upgrade all walls and towers. Get 4 docks and upgrade to the highest war ship. I recommend being a culture that has heavy catapults, ballista towers, and all war ships, like the Greek which is the only civ that has all of the requirements. Put out war ships as soon as you can. Spread them out. Build towers in every open spot behind the wall. Also build your army and empire is the middle of the island. The purpose of the walls and towers is to not allow the enemy to land. Also keep repairing all walls, towers and ships. Replenish ships to guard the walls. To see about ship attacking see SHIP TACTICS.