Are you a Martian? If answer is no! Then don’t write about Martians. Instead, write about something you actually know about… don’t write about stuff that is outside of your own experience unless you’re prepared to do a lot of research.
I will reiterate this statement throughout this guide because it is probably the most important statement you can make when approaching a film, please, for your own sake, “keep it simple stupid!” Write about what you love, what you’re passionate about. Everyone is unique and has special interests that they find pleasure in exploring. Figure out what yours is and see if you can’t find a simple story in there somewhere. Whether it’s a concept, a notion, a character, a love of the pottery, or the ridiculousness of your day job, if you can structure a story around it, with some awesome well-rounded and empathetic characters, you have the makings for a great screenplay.