When battling enemy ships, aim for the crew. If you can take them all out, you’ll be free to take down the ships without any resistance. Taking out the ship first just means you’ll have a bunch of Imperials trying to board your ship.
Don’t forget that you can pluck enemy cannon balls from mid-air by touching them. It’s a good way to stop a shot that would have otherwise hit your ship, and you can fling it back at your foes.
It’s best to save up for new ships before buying other expensive upgrades. Try to get the second ship and the double cannons as soon as you can, as having double the firepower makes a big difference.
Look for the weak points in enemy structures and aim for them first. Since the Imperials themselves will usually be out of reach, aim for some explosives or a supporting beam to bring the whole thing down.
Always plunder. You aren’t coming to the islands to make friends. Be a good pirate and take all the loot, leaving no witnesses behind. If you can shake some of the villagers down for more loot, that’s even better.
When battling the sea serpent boss, keep firing behind your ship. Even if you can’t see it, you can still hit it.
Be very careful with enemy ships that have powered-up cannons. They can chew through your hull faster than you’d expect. Play it cautiously and try to stay out of reach of the enemy cannons.