Were I Satan, I would convince the world that there was one or more all-powerful and all-loving gods, stronger than evil, and a heaven or similar state for those who are faithful to the obscure and often contradictory rules of those gods.
I'd know I was getting all your souls in the end anyway, since I made these "gods" up and there is no Heaven, I start a lot of trouble amongst those who worship different gods or who worship the same god in different ways, and I get to see the look on your face when you die and I tell you the truth: Your efforts and sacrifices were wasted, the one chance you had in eternity to live it up and enjoy, and you denied yourself in the name of following a set of arbitrary rules in order to appease an imaginary creature. God doesn't love you, and any love you feel for him is utterly, laughably meaningless.
Then I get to torture you for eternity. It's win-win-won.
Maybe the great trick Satan ever pulled was not convincing the world he doesn't exist, maybe it was convincing the world that God does.