There's no real guarantee or method to get the max starbits for a mission. But as you build fans to raise your maximum reward it seems to average out a bit higher, or at least that's how it seems to be in my experience.

I've got it down a bit to a method that I just tend to follow. Highest mission I can do for 100% energy, then the beginning missions in the first two areas to keep ego gain low. This helps with trying to find pizza slices to get your energy back to 100%. It's not full proof, but it feels fairly consistent.