A battleship is required for this trick. First, purchase any goods in a store and go to the island where that product is contraband or illegal. After that, talk to the smuggler in the tavern, fast travel to port, get on your ship, and sail to location the smuggler told you to meet someone. After you sell the goods, six solders will appear. The officer will talk to you. After talking to him, the troops will draw their swords and attack. Kill them all, then go to your ship. When at sea, there will be three frigates all named Dolphine. Sink them each for about 6,000 experience each.
Enable the "Immortality" cheat and go on to your ship and find a storm. When you are in a storm with your ship, you will automatically get experience points. Since you cannot die, you can keep accumulating the experience.
Go to Port Royal and go to Fort Charles, then to the hanging station. Attack the level 14 to 18 grunt and he will not retaliate as long as you are on the platform. If you step off the platform, he will start attacking and getting veterans to help.
Go to a house or building where there are guards. After you kill the person, stand in a corner off to the side and wait for them to respawn. When they respawn and don't attack immediately, you can remain still, heal yourself, and voodoo.