How to use chariots is pretty straight forward. Send them against enemy cavalry. Sing their praises. Move them behind the enemy lines and pelt them with javelins, and threaten a charge. If a unit is wavering, charge. Worship them as the gods they are.

You can also use them to break up an enemy formation so that your infantry can exploit the holes. Works pretty well when it goes home, but is a little bit more risky. Don't let them get stuck in the melee, and run them out on the other side.