I love to Play as France in this gam, and i have more than 6 sucsesfull long campains with them on VH/VH only. So in order to win you must have few things in mind:
1- turteling as France is nearly inposible. HRE, Denmark, Milan, England, Sicilians, Mors and so on will attack you right untill turn 40, no matther what you do. So be ready and take the war to them. In fact I dont feal secure (relativly) untill i have 20 provinces in Western Europe. Once the war frency starts you will go in to total war until you conguer allmost entire western Europe.
2- Make the pope hapy. Use crusades to the maksimum, fight only excm. nations. In case you fight another good catholich plane for a blitz war in one- to turns. This means you will need siege equipment, spies and assasins.
3- Use a lot of spies to guard your generals and cities, to spy on the enemy and to open gates in sieges. I allways try to have a spy in each of my cityes and castels all the time. Use a lot of assasins to kill enemy assasins, inguisitors and heretiks. And whatever else you like. In all my games Paris is building assasins quild.
4- Caliary and Ajacho are a AI magnit. Everybody wants them. So give them to the pope. he will love you for it and half of the catholicks will be excomunicated becouse of thise 2 puni islands.
Otherwyse your early game is very good. i just need more agents.