I have evolved my own tactic. Basically it's pin and flank minus the flank.
My typical army consists of three units of spearmen, a couple decent infantry, a few archer units, and two heavy cavalry. Sometimes I also have some horse archers.

Now, when I have to attack an army, I'll spend a few minutes getting them into formation with the three units of spearmen deployed about 2-3 ranks deep along the front line, and archers either in front or behind. My heavy infantry is usually deployed about 5 metres behind my spears, holding position. My cavalry will be deployed a fair distance behind them.

Anyway, I will march in formation until I'm just barely in archer range of them. Then I open fire with my archers, usually by this time the enemy will be marching towards me. Once the enemy begins to charge, my archers will cease fire, then my spears will hold position while the enemy charges into them.

My spears should manage to hold their ground, and the enemy will get worn down after a few minutes and waver. Any attempt to flank my troops will be intercepted by my infantry. After a few units have begun to retreat, I'll send in my heavy cavalry. My spearmen will very rarely waver, and in formation can hold off as many troops as the enemy throws at them. They do tend to suffer when charged by cavalry, though. Oh, and if I bring horse archers along, I use them to lure a particularly powerful unit away from the group. Alone, they can't destroy the unit, but after the main battle is over I can send reinforcements.

This tactic is definitely the one I use the most. It may be complicated to describe, but to me it's second nature and works very well. Still, one day I may get the crap beaten out of me and need to change tactics.