In Aristotle's categories, “Simple” plots involve a change in fortune where there is no recognition or reversal. “Complex” plots include a recognition and a reversal that turns on surprise. The “Complex” plot is superior – in tragedy, anyway.
It’s possible to get too complex, however. Novelists can get into a problem when they have too many characters, too many incidents, too many recognitions and reversals, just too much happening. Aristotle’s antidote: create a pitch. Come up with a compelling three-sentence summary of your story that’ll make an editor cry. Well, he actually says this:
“The plot should be so framed that, even without seeing the things take place, he who simply hears the account of them shall be filled with emotion at the incidents.”
So think about how to describe your story to a friend in 30 seconds, in just a few sentences. This will clarify the story in your own mind. It might help to identify any clutter you should cut. And it will prepare you to pitch the book to agents and editors later.