Napo: Total War is awesome. Make sure you have enough infantry. I've seen a bunch of AI/real people use tons of cannons and I kill them. The cannons are pathetic when the enemy reaches them. Make sure to put several horse regiments on the sides of your army, and make sure you have reserves in the back. Make the front ranks at least 3 men deep. Use firing techniques, such as fire-by-rank. Do NOT let the enemy start forming the crescent shape around your army, because you will die. Keep your troops moving and keep an eye on all your regiments, or all kinds of bad stuff will happen. It's very easy to get preoccupied watching one specific regiment kick an enemy regiment's butt, butt elsewhere, you could be getting wiped off the planet. Whenever your army starts wavering, send your general into rally mode and have him ride around, even if there's a chance he'll be shot. I've won many battles solely from keeping my officers on the move and inspiring my men.
And you better be playing as France.
EDIT: Oh, and always put your best men (such as the Old Guard) in the center. You need them to form an anchor or your forces will be cut in two. Plus, use skirmishers and jagers a good way ahead of your army on the fields to pepper the losers that send regular, range-limited, musketeers ahead first. After you kill a crapload of them before the skirmishers come into their range, withdraw them to behind your main army.
I still remember the discussion me and Napo had about total war
What you talkin' 'bout, Willis?
EDIT: Holy crap. Gangnam Style has 1,000,000,000 views on YT. Can't say I'm not happy.