[Verjigorm]

You have to play against a person to really learn it. The AI's tactics are mediocre at best and seems to lose steam somewhere in the turn 30-50 range, and there's no diplomacy to speak of. Just join an MP game and then ask strategy questions in the appropriate section of the forum which... I can't remember where it is just now...

The best way to play is to be like Water (no, I don't mean take a bunch of picks in Water magic), but be fluid and react violently to the motions of your opponent. Break before his advance and swallow him from behind, etc...

No one ever always wins. Much in this game depends on the advantage of initial positioning and a number of other factors such as who you get for neighbors. Dom3 tends to exhibit circular dominance patterns like Nation A kills Nation B and Nation B kills C but C kills A. Thus depending on who gets dropped next to who influences the outcome greatly as do the personalities of your neighbors.

Ten tips for any TBS:

1. "So it is said that if you know your enemies and know yourself, you can win a hundred battles without a single loss." - Sun Tzu (In Dom3 language it means use lots of scouting either physically or magically. I love Stone Spheres. Eyes of God on Immortal or recuperating pretenders or when you have healers is also great). LA Man's Magisters are my absolute favorite spies of all time. +25 Stealth, spy ability, and they count as 16 dudes for siege or defense.
2. Never throw your army away. Land can always be retaken.
3. Use small things to control large things.
4. Save for a rainy day.
5. Don't let the enemy see what you are doing. Patrolling a choke point (Great Eagles, Simargls, Judges, Machaka Eye of the Lord or any unit with a patrol bonus) can prevent spies from entering. As a bonus, such patrols are also a great addition to blood hunting provinces and can net you a touch more income from states in which they are conducted. You can micro manage tax rates above 100% in patrolled states especially if you have growth scales.
6. Move in unusual or unexpected ways--if he is watching you, use that to your advantage. Try to control his thoughts through your movements.
7. There is no such thing as a strong ally unless you have a team victory condition.
8. Do not play your opponents game. Make him play yours.
9. Easily obtained food looks tasty but is frequently poisoned.
10. "War is simple, direct, and ruthless." -- G. S. Patton