4. Throw A Wrench In The Works
Let's imagine that you've written a good, solid screenplay, but it's missing that "oomph" factor - one which helps to differentiate it from other good, solid screenplays (which there are, like, a million of). Your best bet, then, is to take a long, hard look at your finished screenplay and see if there's room for you to factor in another unique story aspect. It might mean that you're going to have to re-write lots of the script, but "throwing a metaphorical wrench" in the works can a) mark your screenplay as something special b) inspire brand new ideas. In the case of
Prometheus, the "wrench in the works" is the android David, who exists purely to create a mayhem and force the other characters into the movie's situations and set-pieces. Despite being played excellently by Michael Fassbender, Davis is a great writers' tool because his motives are all over the place. This doesn't work quite as well as it might've because
Prometheus is all over the place, but the movie would have been rather dull without him. Factor in your "own" David - it doesn't necessarily have to be a character, but could be an item or a new plot twist - and see what happens. It might not pay off every time, but it's certainly worth the risk.