Write, direct and produce as much of the film as you can on your own. Unless you have talented friends willing to work for little or no money, or willing to wait for a share of the potential profit, you're going to spend some of your budget on these things. By doing as much of the work as you can on your own, you'll have more money to spend on the actual shooting and final editing of your movie, which will greatly enhance the film's attractiveness as a profitable package. Put together your budget ahead of time.
Start with the script. You need an engaging story, but there are some other factors to consider. You want to shoot a low-budget movie. The script should use as few actors and locations as possible to tell your story. A script you can shoot with just a few actors in a single location will be cheaper to film than a script with 50 actors who need to moved between locations. Other considerations are important too. Try to avoid night scenes. Shooting at night takes lighting, and lighting adds expense. Take into account every single prop you will need as you write or read the script you want to film.
Audition actors. Hopefully you have friends or family with a little acting talent who might be willing to star in your movie on a share-of-the-profit basis. Make sure they can really act. Don't hire them if they can't, even to save money. Poor acting can destroy a film.
Gather your equipment. Unless you already own a movie camera, or know someone who does, you're going to spend a little money here, even for the lowest grade camera acceptable for shooting a film. You could use a digital hand-held video camera, but you'll end up with a film more akin to a home movie than one worthy of a big screen. Other factors here include lighting and various devices to facilitate shooting a film. Smart shopping and ingenuity come into play. If you know someone handy with tools, you can make a steadycam for around $14 (see Resources).
Edit the film. This will consume a good part of your budget. Unless you know what you're doing, you'll want to find someone who can edit. Editing the film includes color correcting, checking for continuity, and cutting and piecing the footage you've shot into a finished motion picture. This is usually done with a computer and film editing machines in a studio.
Market your film. Shop it around, as they say in the movie business. Use the film as your ticket to the big time. Get a website to promote it. Check markets and try to get your film viewed by industry professionals. This could lead to work with big studios. The best way to market your film is to enter it in contests and show it at film festivals. These avenues often lead to major movie deals that can set you on a successful career path in the movie business.