As implied above, I think one important element here is to throw Palpatine some curve balls. He has plans, and, while he will come out victorious (obviously), even he needs to be foiled every once in a while. Through opposites doeth the path proceed. I'm thinking of tensions between him and Darth Vader's predecessor might be one good way to go, but also just having the Senate or others refuse his will here and there, just to show that his ambition does run into obstacles and barriers that he needs to overcome. This is something I'm thinking of particularly for Ep 2, where he has a much more central role to play, being the Chancellor.