You wanna get those cities and make Baron in all the powers within 12 years game time? I got it down pat!
Start off any power, but you want to work your way up north as soon as possible, try to bag any pirates along the way so you build up good cash flow. Stop by Spanish ports along the way and do missions for their settlements and with the immigration atFriar Tuck's so you can get rank and score cheeser points before you unleash a "shock and awe" upon Spain. Somebody is always at war with Spain, and my first target is always St. Augustine. I also look at the map and pay attention to "settlements" that are nearby that may be with the power I want to install in the city I take. After taking a Spanish city I make a trip to a settlement and install a governor (though they will do all that on their own in time) and I visit Friar Tuck and try to bag an immigration mission and put them in the city to help build it back up.
St. Augustine is easy, now for the hard work, taking out the Gulf of Mexico cities, Havana, Santiago, Santo Domingo, and San Juan (I'll explain why later). If I do not have a large force, I stop by EVERY Indian place and pirate base along the way, and tell them my target city is ripe for an attack, even if they fail, they still wear down the defense forces. Also ALWAYS kill troop transports, you do not want them reinforcing anything in your area. I also try to engage every invasion force as well, they pay good, and I want credit for taking a city, not the power I work for just sneaking on in after all my hard work and claiming the glory. Also, if you see a settlement near your target and they are not at war with Spain, give the city to that settlement's flag. They will reward you anyways and you can make a trip for gov or seedlings and score cheeser points.
I do not bother dancing with just anyone anymore. I've learned the plain Janes only give items, heck, I can buy those from the tavern. Attractive women give you the "wanted" people in other cities. Waste of time unless it is a target city of mine anyways. The beautiful women, that's the ones you wanna dance with. They tell you were Raymond is, and also where Montalban is sometimes (Abbotts do the same when you have a relic sometimes).
So, the whole northern Spanish sites are shut down, as well as the Gulf of Mexico (By this time you should have made Duke in some powers, and also have engaged most pirates already, giving you awesome cash flow). No more sailing everywhere looking for the key players, they will always be on the southern main going from Spanish city to Spanish city. I usually take out the western edge to near Rio de la Hacha, but I always leave Maracaibo and eastward alone (I do take out Gibraltar as it is a pain in the arse to sail down there looking for one of the key bad guys.).
DO NOT TURN ON ANYONE until you have gotten Montalban and your relatives. Like I said, you are already a Duke in every power but Spain, and no need to piss them off yet. You should be between yr 10 and 12 by now, you have 8 good years left. Now I start dancing with only beautiful women, and they give me pieces of the 4 lost treasures. Make sure you look in your map and pay attention to what cities have beauties. Find a beauty to marry, the bad guy that keeps them on his ship follows the Spanish trail pattern as well going from only Spanish city to Spanish city. Believe it or not, I think the Spanish women are the "hottest" and I do small favors for Spain getting ready to turn on the other powers, I've even managed to marry one in the game. Usually the lost cities are on the western part of the Carrib, so you can save time from sailing everywhere by being near and finding beauties nearby. It doesn't matter that you are married, they love giving up the poonernanny and pieces of lost cities maps anyways.
Once you get your relatives and take out Montalban, the lost cities are too easy. After you find all 4, even the beauties will start with the items or "wanted" people as there is nothing left to get. I also noticed that if I already have a full map of a lost relative or Montalban's hideout, they still sail in my limited "area" and I can keep bagging them, that's 3k and 5k a pop! I've also played it out so Mendoza showed up 3 times as he had 3 different girls.
I know there are other plans that can work, I just thought I would give some tips on how I play it out. I've noticed 2 things that suck, IMO. The land AI is crap, I hide my officers in trees, and place my musketeers 1 square behind them or nearby, and the enemy will ALWAYS go for the closest target, except for the Indians sometimes, and the enemy cavalry never cooperates like that, they like to go 3 squares at a time and they look for your musketeers.
Another thing that sucks, and is a bug, is when doing a Gov or immigrant mission or seedlings, I get engaged by 2 ships average at same time. I blast one real good and he surrenders, but still fires at me and attacks me! I've leraned to try to engage them before they get near each other, sort of like when you want a prize and another enemy or pirate is nearby and they get "sucked into the mission" as well as the target vessel (If only we had that kind of luck on SFC OP!).
Oh yeah, once I'm a Duke? I take out their treasure ships and military payroll ships, you have nothing to lose anymore. I just leave the cities alone until I have all I want, after that, who cares if Spain gets them? You have already bagged all there is to get. Then I fight like Hades for Spain, and you will make Duke well before you are ready to retire.
My best score (ALL Governor) out of my 3 finished campaigns? 122.