I get into some serious ruts during troop production phases, so I tend to have armies with a lot of the same units (I never play MP...)

However, when I have a mix of units, I tend towards these strategies:

First, I always start with the archers in front, move them back when attackers get near.

Now, the options I decide between, depending on the enemy army size and composition.

1) If the enemy has a lot of tough units, I try to spread the shock troops a little bit amongst the typical HtH guys, but leave a few to the far edges for a flanking encirclement.
2) If the enemy has a sh!tload of archers, I put the cheap, well-armored guys up front and leave the shock troops behind on the flanks, as well as directly behind. Then when we get up close, I hold with the Yari, cover weak spots with the shock troops, and flank like crazy.

Duff