Informants : When you meet a governor's daughter, she might decide to become your informant. Visit her often : she'll have important information on the location of the Silver Train and Treasure Fleet. Warning: if the governor loses his job, however, he'll return to Europe, taking your informant with him !
Lost Relatives : Find all the lost relatives you can! They often know where hidden treasure can be found.
Growing Old : The older you get, the more difficult it is for you to swordfight. You'll want to have more men with you when you attack, because it will be tougher to win. Eventually, you'll grow too old to continue and you'll be forced to retire, so don't waste time while you're young !
Selling Ships : Sell your cargo before selling your excess ships.
Gossip : You can learn of goings-on in the Caribbean at the tavern and by "Hailing" other ships for news. This news is recorded in your "Ship's Log" in the Captain's cabin. The things you learn can be very useful. For example, if a city has been hit by a disease, it will probably be weak. If gold has been discovered, it will be rich. If the city has a new governor, then any informants in the city are gone. And if one country has gone to war with another, you can probably purchase a Letter of Marque from one of the countries and get rewarded for attacking the other.
Large Crews : It is really tough to keep a big crew happy for more than a year. You'll have to keep getting bigger and bigger treasures, plunder really rich cities, capture fat Spanish galleons, and so forth. Once your crew begins to desert (taking your money with them!), either grab some big treasure fast, or divide the plunder immediately. When you divide the plunder, you lose some time while you refit for the next mission, but you'll get a bigger slice of the treasure.