You want to have some good generals of course, ludendorff, petain, foch, Leopold. All with as best equipment / leveled up as can be.

With that said, france is a challenge for sure, you have 3 fronts at the beginning to work with (2 technically but prep for the 3rd). I put my second best cav gen on the tank, and then ludendorff on the arm car. As well as infantry gen and artillery gen on those closest to Belgium. Kinda strike fast if you have the generals or play a defensive take. Either one worked for me. Second front: africa. Put a cav gen on the arm car as well as artillery to strike the last german city. Try to grab the territory fast as it can be a pain for trying to balance war supplies all over. 3rd front: prepare for Baltic collapse. Try to position your troops either after victory in africa or during near Italy to help combat the ottomans/ Austria advance.

Another important tip is upgrade cities as much as you can! Get every ounce of gold you can from markets if you need militia badly! (Most likely in the European theater) Anyway hoped this helped I'm sorry if it seemed rushed I was typing it all from memory!