Let's write a nice story.
When entering a battle. you have a personal cavalry (general bodyguard). Just let them follow you. When having large amounts of cavalry, let them run behind the enemy. Now set up ur infantry ranks and hold fire.
After this, let the infantry walk towards the enemy. When close enough. FIRE!!
That's ur first volley =)! The next stage is to let ur cavalry attack the enemy in the back.
Finally, retreat them and join them. Now let ur infantry attack them with melee weapons. finally lead your cavalry into the back of the enemy. Viva 19th century!
And that's only the field battles. Ever seen a fort battle or the coming naval battles (maybe)? Also seen my beautiful houses in the cities? Also did you finished the quest of the Cathedral of Saint-Étienne?