Any universal strategies, or rules of thumb?

[For Victory]

I have installed this game as well as kingdoms and I am enjoying it although I am having a heck of a time getting good at it. I was wondering what necessary tactics there are for the campaign map that you can use for any faction. For example, in the first turns of a campaign, what should do upgrade/construct/recruit etc? I am new to this kind of game and don't have much common sense for this play style. Secondly, which faction is easiest on a new player? I'm also playing the Stainless Steel mod. Thank you very much.

[Old_Scratch]

Here's one; if you have an upgrade choice between armor and weapon, pick the weapon upgrade. Even though both look like they only give you +1, the weapon upgrade actually gives more of a bonus that the armor upgrade. I'm not saying armor upgrades are useless, far from it, I'm just saying if you can only pick one.

[For Victory]

Thanks! Anyone else? I could really use the help, at the moment I am overwhelmed.

[Viking Prince]

A humble suggestion for the newbie:

Viking Prince’s Strategic Guide for Newbies to Medieval II Total War
Viking Prince’s Faction Strategy Guide for Newbies to Medieval II Total War: England

[Nazgûl Killer]

Victory, I can tell that from personal experience, Viking Prince's guides are REALLY helpful...
However, if rules of thumb are what you're looking for, here are some:
ALWAYS check upkeep and stats before recruiting units, make sure they are good enough/what you want/aren't too expensive.
Captain armies are BAD against anything aside Rebels! Reasons: 1) Captains rebel, A LOT, 2) Captains have no command bonus, however, Captains fighting Rebels can become powerful Generals, so sending them to fight randomly-appearing rebels inside your country can be a good idea.
Don't be afraid to leave your generals behind. Leaving a general in a city is extremely helpful, especially if he has chivalry, if a general, ANY general, is in the city, it gives you a lot more income and if he has chivalry, minus to squalor and a + to population breeding percentage.
Keep your main bloodline pure. If your king has dread, make sure your prince ALSO has dread, that case you won't have to battle it out with traits like "Dreaded Father" to get chivalry, it's much easier and beneficial to get the same dread/chivalry as the father has.
Navies are important, yes, but not with all factions, for example; Sicily cannot play WITHOUT a proper navy, if your navy is weak as Sicily, you're basically screwed as Venice, Egypt and the Moors will eat you alive, however, if you are playing as The Holy Roman Empire for example, having a navy is useless, being mostly on land and easy access to many provinces via land battle gives you no need for a fleet, could just be a humongous waste of money.
Navies transporting armies should never go below 4 units, the reason is, think of it this way, you're transferring an army of 1200 men, in them your Prince and King, on one ship... Guess what? Rebels attack you, bye bye. That's why you need, at least, 4 ships at a main navy, the navy who fights/transfers, and if you don't want to waste so much money on so many ships, MAKE SURE you have a strong navy, at least one, and use him to transfer your troops, this way you can either win the fight, or just scare off any AI opponent from attacking you.
Trade is IMPORTANT, trade income (Without merchant) Can reach to the hundreds of thousands, so improving it by buying fairgrounds, merchant wrafs, ports and roads can be very beneficial, building a trade empire isn't too hard and it gives you a lot of money. The way to do this, build ports where important trading sites are (Example: Naples or Venice are in the middle of a thousand ports, so they will be a grand trading site, however, Jerusalem hardly has anyone to trade with, and not only that, its land trade is MUCH better, so building there will be a waste), trade can be your main source of income.
This should get you started well enough... If you want more advice, PM me or something, or go read Viking's guides.

[Commander5xl]

Yes VP's guides are amazing

[Muagan_ra]

An economic suggestion - don't be tempted to convert too many settlements to castles, just to access the supposedly better military units they have.

Too many castles and not enough cities will absolutely ruin your economy, and you might find it hard to make enough florins to support your empire. Try to have one castle per "region" - one on each of the frontlines of your empire, where you will actually meet the enemy. No point in producing military forces far into the heartland of your realm.

Many factions have militia units that are far superior to most of their castle-trained units, like the Italians, or the Turks.