Save cannon fire
If you lots of money, buy cheap fire pots and chain ammos. In a battle, click the "Fire Pot" and "Chain Ammo Throw" buttons continuously. By doing this, you will hardly have to use any cannon fire.
Trading contraband safely
Build your dynasty early to achieve greatness later. You can get plenty of tasks from all the Governors. Build yourself up to at least three or four tasks, then stop. Do not fulfill any more tasks for awhile. At this point build up your money. Travel back and forth between two or three cities and trade products, buy bigger ships and fight more pirates. This will take some time. One advantage is that the pirates you fight will stay the same. They will not advance in strength until you complete more tasks. Once you accumulate 50 million gold begin to freely advance. Note: Purchase the Port Authority Ragdoll. There are two versions which cost 50 million and 100 million. They will allow you to safely trade "contraband" in any port.
In any port, visit the bar and buy a round of drinks. You can get information from the bartender. The bartender will tell you what items will be contraband in various places and when this will happen. At first, you can only have your warehouse in Port Royale. When you get money from fighting or trading, invest it to expand the warehouse. The maximum size you can get is 9,999 storage space. Once you have the information from the bartender, buy those goods and save them in your warehouse. When those items are considered contraband, go back your warehouse and sell them. For example, suppose that wine will be contraband in May in Port Royale. Buy wine in advance when it is cheap enough (5,500 or 6,000 gold). In May, go back to your warehouse and you will notice that the price of wine is very high because of contraband status (at least 13,000 gold).