Choose what horror films you want to parody. You can pick a specific film as the main focus, like "Saw," and then mix other horror films into the plot. You can also stick to a specific horror genre and focus on supernatural, slasher or science-fiction horror.
Analyze the films that you want to parody. Take notes of key scenes and dialogue you want to touch base upon. Write down quotes that you can turn around and make funny. For example, you can start a scene off with the serious scary tone and then insert an unexpected object, like using a kiddie ice cream truck instead of the rusty, run-down, and truly frightening truck from "Jeepers Creepers."
Write out a script. Even though it is a parody, it should still follow the three-act structure and follow a storyline, even if it's copied from the original storyline. Treat the characters as you would if it were a serious movie and not just a spoof.
Scout out the locations. You want to capture the feel of the original horror movies because the more authentic the shots and locations, the more the comedy will pay off in the end.
Choose whether to use pop-culture references or keep them out of the film. It's easy to make jokes about current political and Hollywood situations, but in two to five years the jokes will be out of touch with the audience. Using pop-culture jokes could make the movie feel current and expand the possibility for jokes. For example a character could appear scared of a horrific monster until another character walks on the scene and explains that it's just Lady Gaga.
Use actors that look similar to the parts you parody. Like the jokes and locations, this will only serve to make the parody more convincing. The basic height, hair style and clothing style are key features to focus on, although they do not have to be clones of the other characters.
Work on the ending of the film. This will be the opportunity to make the parody a success. Take the ending of the original horror movie and offer up a new twist or solution that will shock viewers and provide comedy. For example, in "Scary Movie" the Dewey-based character (from "Scream") named Doofy ended up being the killer.