Some tips, dude:

- As Cynwulf has already pointed out, matching up troops is essential. Learn which of your units are good against specific enemy unit types and you will fare much better. (For example: 1. Spears or polearms against enemy cavalry 2. Swords against enemy spears 3. Lightly-armoured infantry against enemy polearms 4. Axes against heavily armoured infantry)
- Pay attention to enemy valour before you hit the battlefield. Yeah, maybe they’re only feudal sargeants, but if they’ve got 5 valour, they will butcher your CMAAs. Bad match-up, haha...
- On defence, the ole “half-hex” of spears/polearms protecting your archers on a hill makes a good formation (keeping fast shock infantry and cavalry on the flanks to counterattack).
- On offence, try to break up the enemy formation by drawing units out with missile cavalry before you launch your main attack. Charge vulnerable and exposed archer units with cavalry to make the main assault less costly in terms of missile damage.
- Try to maintain an advantage of manoevrability. (ie: Don’t pack an all-infantry army against an enemy with lots of cavalry, as you’ll never catch them.)
- Cut off the serpent’s head!! If you see the enemy general wandering around by himself, try to kill him before he can be supported by others.
- Maintain a terrain advantage wherever possible. Even on expert, the enemy can sometimes be drawn into narrow passes and ravines. Give your archers as much time as possible to tax the enemy before melee is joined in earnest.
- PAUSE. Pause is your friend, especially when everything starts to go a bit chaotic and you need to get your head together, or when the battle is spread out over a large area. The camera can be a bit slow sometimes. Hit the pause button and deliver multiple orders before rejoining the game.
- If your general is inferior, your army is smaller, and your units are inferior, just walk away. Even if you choose to go to the battlefield just to see what his formation/position is like, you can still walk away. No harm, no foul. Just plain, sensible Sun Tzu.