Scout for a good location for your horror movie. Consider all of your friend's homes to see which one may be suitable for filming. An older home or one with a lot of light may be good for filming daytime shots. Dark, dreary homes may be best for horror movies shot during the night. Pick multiple locations if necessary and coordinate with the home owners about times when you can use the home without interruption.
Consider your friends for roles in the film. Homemade horror films are usually made on small budgets or no budgets at all. Use your friends and their friends and neighbors for various roles. Consider the personalities of each person when casting specific roles. Smart, funny people should play those roles in the film, while serious looking or sarcastic people will make great villains.
Secure whatever equipment is necessary for the filming. Handheld DV cameras are great for fast paced shots, just make sure you hold them steady. Use tripods for steady shots and get as many lights as you can. Renting equipment is an option if you have a budget. Multiple camera angles will add to the professionalism of the movie, but renting additional cameras may require costly deposits.
Obtain props for the movie. Horror movies often use fake blood, weapons and other props for effects. Go to Halloween stores or hardware stores for tools. If you have a prop store or a place where you can buy latex and other makeup props, visit it to get some good advice from the people who work in the store.
Practice each scene, carefully following the script. Practice and evaluate the acting and what does and doesn't work on camera. Although a homemade horror movie is low budget, it doesn't have to be low-quality. Rehearse as much as possible while also staying on time for the filming process. Film the rehearsals if possible and watch them to critique the action.
Take multiple takes of each scene for editing. Use the best scenes in the movie and try different approaches each time as they all will not work, but one may be far better and make the film that much better.