There are a couple of national goals that will help you gain lots of perstige. The first is to build the panama canal and the second is to build the suez canal. The hardest part of both of these tasks is to capture the area. For the suez canal I would reccomend using your troops stationed across the mediteranian in morocco, because is takes so long to go around the mediteranian sea. Building the Panama canal is a little harder. one good tip is to bring a lot of troops when you are attempting to capture panama because If you fail to capture it you cannot postpone them taking it back with small squads, you have to cart your troops all the way across the atlantic and that takes time. You should make alliances with the papal states, switzerland, and some of the other countries that are surrounding France. This makes it so you don't need to worry about the surrounding countries attacking you and it also gives you allies for protection (not that you need any protection, but it's a good addition).
As we sped up time with france we made good decisions that were good, so our prestige went up by like 20 or more withing a year.