Hey Chiel,
Welcome aboard.
As a fellow Sous-Lieutenant, my number one tip would be patience, both in attack and defence. It's rarely worthwhile attacking before you are ready, and wait for the enemy to come to you when defending. You wont ever win in a turn, but you can easily throw away an advantage in a turn by over committing units.
In conjunction with that, try to keep your higher level units (brigades/divisons/corps) organised. The individual pieces are building blocks for higher level formations. Think of them like bricks in a house. Isolated units are prone to destruction, while masses together fight better.
Learn how to use skirmishers especially in defence. They don't necessarily produce lots of casualties, but they can severely hamper any attack. Be carefull because cavalry can overrun them without breaking stride.
Finally, be aware of the Rock/Paper/Scissors nature of Napoleonic warfare. Victory comes more regularly through the use of combined arms, rather than trying to have your infantry slog it out in massed frontal assaults.
Hope that helps
Vive l'Empereur
