Chartiots are the best units in EB.

One unit of those in my stack and I can win any battle.
They kill over 200-300 enemies easy each battle, while taking only 2-5 casualties (hugh unit scales).

1. Deploy them behind your lines. Do NOT let them enter the fray. Just let them scare the enemy.
2. When the enemy is weakened and demoralised, click behind the enemy lines so that your chariots go through them.
This will most likely cause a massive rout.
3. AND MOST IMPORTANT : Keep the chariots moving at ALL time!
Imagine you were a foot soldier :
a. you see a chariot charging at you = scared
b. you see a chariot standing still in front of you = you pull the enemy of the chariot and kill him.
4. Chariots are good against cavalry, but keep in mind : keep them moving!

Summary :
Use them to demoralise the enemy and use them to initiate mass routs.
And keep them moving!