For new writers say you’ve written your first script or first novel and whether or not you’ve sold it you are usually thinking about the follow up story, or sequel. Remember this. Your first story is a moment in time. Something will have happened before it and something will happen after it. When creating the continuation of this event that continuation has to be free standing. If some one gets the second novel or watches the second film they really need to know where it came from. Here’s the tricky part in the beginning you need to revisit the first story, but you can’t bog down the second story with it. Choose carefully how you do this. The most important thing is whatever you do, it has to make them want to read or watch the first one to find out in detail how all of it came about.
One method I’ve seen is to embed small events from the first throughout the second. Where that helps the folks who haven’t read or watched the first one it generally bores those who have.