Just do all the things from the first game but better.
Hey, Evan Almighty wasn't too bad, just not as good as Bruce Almighty, which rocked.
If you want a good example of bad sequels, look at horror movies.
It's okay to have some alright movies that don't beat the first one (Saw movies), but if you try and make one better (Nightmare on Elm Street 2, which fails at this), you should take a new angle on it (NOES 3, goes for more comedy than scares, kicks ass).
Alexp pointed out that although DZD 3 was fun and stuff, it wasn't as funny as the previous games. I fixed it up a bit, made it funnier, and there you have it, better than the last two.
Keep the good stuff, increase it, kill the bad.
This is the key to sequel making.