The Spiral
On this map, it is vital to maintain the sea. There isn't much room to hide a transport if you are knocked off. If you've won the sea, and they are still on their first island, use your battleships to destroy their gold mine on the outer edge. This will ensure victory for you.
If you know your opponent is beside you, take the oil patch between you. If he happens to build on that side, he will find himself in trouble with a long way to go for oil. Then he'll have to spend the extra time and resources to stick up another on the other side of his island.
Move peasants around early. If there are only a few players (2-3) you can quickly colonize and have 3 islands to their 1. This also gives you new bases for shipyards. Make sure to protect these settlements though.