One of the advantages of a Franco-German alliance is that it can last for a long time, as both Germany and France have their own area of expansion.
The first mission is to eliminate England, which can be hard. There are a couple of tricks to get rid of England fast(er) but it will remain a tough job. However, once you have secured your backs, you can spend all your energy and units focusing on the Mediterranean as France, and on Scandinavia and Russia as Germany. Another advantage is that with these two countries chances are quite high that you easily cross the stalemate line.
Germany is surrounded by England, France, and Russia. This assumes that Austria and Italy do not make an early move against Germany, which is true 99% of the time. To build trust between France and Germany you need to agree on a DMZ in Burgundy (or a prearranged bounce) and agree on who is going to conquer Belgium. If you do not find a method to divide Belgium in 1901, it could be an option to leave it empty.
To start a successful attack against England Germany needs to build a new fleet in Kiel in 1901. An attack on the North Sea can be made with the help of France on the Channel. I would normally divide the English supply centers in such a way that Germany takes Norway and Edinburgh, and France seizes Liverpool and London.
France has many options in the beginning of the game, not least his two Iberian supply centers that he can grab. An alliance with Germany has advantages over an alliance with England, as Germany is less likely to stab France than England in the middle game (1903-1906).
For France, the start of this alliance should be very simple, but France wants to have guarantees that Burgundy will remain empty. So I can imagine that you propose a bounce in Burgundy playing France. The nice thing playing France is that you do not need to be very hostile against England in 1901; even a DMZ in the Channel is fine. After 1901, building a fleet in Brest is crucial to defeat England. Notice that combined with Germany you will have 4 fleets, where England only has three.
Longer term the way forward for France is clear. An attack on the Mediterranean region has to be the next step. I believe this is what I like best about this alliance both from French and Germany perspective. Once the first three years are settled and England is defeated. Nothing stops you from going all the way for a duo or three-way victory. Stabbing each other is possible, but not that simple, as the route via land is only via Burgundy.
The only downside for France is that his fleets are probably further from home than the Germany fleets, which could be a downside in a potential conflict. Still, this is one of my favorite alliances if you manage to survive the beginning together playing Berlin and Paris.