[TLDR]
1. Get a ship
2. Raise the Difficulty to Adventurer
3. Get a huge crew and a hauling ship
4. Raid a port on the spanish main and give it to the Dutch.
5. Raid from the spanish main until your crew gets sad
6. Dump all your food and travel to St. Martin to Divide the plunder
7. Travel to all the friendly ports on the way to your raiding city hiring people and start over.
[TLDR]

The game starts automaticly in 1660. You start with a crappy ship and almost no money or crew. Your first goal should be to get a better ship. Here are some good chioces.

Sloops and Brigs are very fast and manuverable. It makes catching small weak targets easy and are actually the 2 best starter ships. You can use these to get yourself some stupid merchants and smugglers quickly. They have alot of crew so catching and boarding are easy.

Galleon's are slow but pack a huge punch. They can fit alot of cargo and people so its good to have one in your fleet so you can store your goods and raid ports.

Frigates are what you should be shooting for eventually. They are fast, pack a punch, and are very manuverable. They are honestly the best ship in the game because they are the best all around ship. But its not gonna happen in the beggining of the game. Frigates are rare. If you see one go for it. Its ussually named New Warship and has some great named versions out there as well.

What i do is find a Brig of War or a Fast Galleon right away.

Now that you have a ship its time to increase the diffuculty to at least adventurer. You are not getting the high score if you play it on easy. Raising the diffuculty level will make the game harder but more rewarding and fun as well as give you a larger share of the loot when you divy it up every couple of years. You will be given this option when you Divide the Plunder at any port. Choosing when to do this is an important part of getting a high score.

When you divide the plunder on Adventurer diffuculty you recieve 20% of the take. Every single person on the ship will get a portion as well. Its the only time you can increase the diffuculty and you may never lower the difficulty once its been raised. You want to have as little assets and crew as possible and as much money as possible before you spit the loot.

Never attack the dutch. No matter what scenario you play in the dutch are always the weakest in the game. That makes them great fall back guys if everyone else hates you. Spanish are always the best targets. France and England I try to stay allied with but its hard. France and England tend to make alliances during the game to the spanish. So they may get upset at times that you are pillaging the spanish main. Just pay them off and keep raiding.

When your crew gets unhappy keep raiding. Don't stop. But start making your way to where you do your recruiting from and stop buying food so people get really mad and leave. Make sure you kill off some of your troops slowly and do not replenish them. By the time you get to St. Martins you will have a tiny crew and no assets but cash. Divide your plunder and then start recruiting and heading back to the spanish main.

Using this strategy you can get a really high score and just keep an eye out after you hit 28 for named pirates and start hunting the quest toons and looking for pirates buried treasure. You want to wait until you are older so the pirates bet bigger stash's, more unique items, and keep the economy in demand. After a couple of years you will get substantially more from these already high value targets and once all the pirates are gone there will be less demand for your stolen goods in other ports. So wait a bit before you decide to blow these guys up.

Hope this helps.