i like using artillery to force the enemy to bring his archers forward, then charge them with the 1-3 cav i keep in my army. After his archers route or die, it forces them to come to me in order to attempt to keep me from peppering them with arrows from a safe distance. Then, i merely set up an infantry line, take whats left of my cav onto the flanks, and have my archers 'focus' fire around the middle of the enemy formation before actually engaging them. Even if my archers only cause about 30 casualties among 2 units, thats still 15 less people my infantry have to worry about, and even with only 5 men left in 2 cavalry units, when flanking, cause a serious morale/damage problem for the enemy lines on the sides, usually causing it to start collapsing.

If i have access to some nifty things like Xbows, i'll have em focus on priority targets while the melee goes on, like the enemy general or that annoyingly deep bulge of enemy troops in one part of the line.