I like to mostly defend, espcially when your terrain has natural choke points (which doesnt seem to happen as often in S2). I agree with dead guy that defending hills is not as effective as in MTW2 and RTW, but there are some hills with only a few paths to the top. I like to fill these pathways with a mix of infantry, have the archers do a checkerboard by having them stagered behind my infantry and some in front and I make good use of the flaming arrow barrage. I will use flaming arrows from the archers behind my infantry to cover the retreat of archers in front of my infantry. While the attacking units slow down slightly from behing hit with the flaming arrows, my retreating archers fill in the holes inbetween my archers behind my infantry. I then like to hide a couple cav units in the trees way in front of my lines to then take out the enemies general or archers...

In normal flat terrain I still go defensive with spears in the middle, 2 samuri behind the spears to plug holes (or use a hero unit for this), samuri on the ends, cav either way way out on flanks or hidden in trees and then use the same checkered board set up to my archers. I always try to have numerical archer superiority so I am not forced to go on the attack.

If I am forced to attack, I split my army in two similar groups, split them to two sides and try to swing one around behind or to the direct side of the enemy. If you do this right sometimes the enemy wont know which to face and with minor movement on your end they will constantly keep rotating back and forth between your two army groups which wears them out. This works espeically well when one or both of your army groups are in trees and can become hidden. Everytime you move one of your army groups slightly and they become visable, the enemy moves. Then when the enemy turns, let your army group they turned to go hidden again and move the other army group and the enemey typically moves back to face them, keep repeating and they get tired. I know... its kinda cheap but you can get a lot of heroic victories this way. I learned this tactic from someone else on the forums, but I couldnt find their original post to give them credit.