I took a narrative theory course in college, and it's always been on my long-term mental to-do list to learn more about the subject. But something I've always remembered is the idea of paratext. The International Society for the Study of Narrative defines it as all added written material included in a book that does not count as the primary narrative. The website TVTropes expands the idea, defining paratext as everything that is an element of the whole package immediately encompassing the text and not part of the text itself. In other words, all that stuff that isn't a part of the show/movie/story itself, but still comes with it. The stuff on the box, the stuff that comes before the show/movie, etc.
Basically, you can't really evaluate a book/movie/TV show/etc. without being consciously or subconsciously affected by the poster, the marketing campaign, the cover, etc.
I think the idea can actually be much bigger. Let's say you go to see the movie Killers this weekend. Imagine all of the things outside the movie that might affect your viewing: ubiquitous advertising, Ashton Kutcher's Tweets, Katherine Heigl's performances in Grey's Anatomy, reviews of the film you read in advance, interviews with either of the stars, similar couple-action movies like Mr & Mrs Smith or The Bounty Hunter, your knowledge of the development of the film, the script, etc. Even if you watch a film or TV show with no positive or negative expectations, all of your knowledge and experiences will frame how you respond to it.
Similarly, your knowledge and experiences will frame how you approach writing scripts. If you've just seen twenty movies with male protagonists, will you be more likely to write yours as male? If you can't find many movies with women talking about something other than men or marriage, will you think to include it in your own scripts? It's not just about gender, it's about the worlds we live in. If you've never taken a bus, will you automatically show your characters driving cars? That's the danger here. What about race? Geography? Occupation? Sexual orientation? When you think of a doctor, do you think of a man? When you think of a couple, are you assuming they're straight? When it comes to race, I like to write my characters with no specific physical descriptions that would pigeonhole them as one race or another...but if you're giving all of your characters Anglo names like John Grant, does that impose an assumption about race or origin?
What isn't occurring to you?
There's nothing wrong with writing about your specific experiences. If you're an expert on something, go ahead and write about it. It's often a good way for writers to begin, and writers are often hired or championed because of something interesting in their lives. I would just love for us to be aware of our perspectives, our biases and the choices we're making.