The easiest way to quickly accumulate a bonus is by taking the Pirate Cove and keeping hold of as many ports as possible. Also, ports are key regions to hold to get around the map, obviously. It's worth noting that ports attack docks, but not vice versa.
Apart from that, use the legend to link up little bonuses and take control of an island. Pirate Cove is the best option, but you'll have to keep it well defended.