Buy yourself a decent digital video camera that has a card you can simply plug into your computer. You might also consider picking up some professional video-editing software, which can range in the hundreds of dollars, but will be worth the money if you're serious about quality filmmaking. Pick up a microphone as well to supplement the one you have on your camera, which may not pick up audio well. A tripod is also recommended.
Write a script. Don't be too ambitious; write one that you can actually film. Special effects are best left up to the professionals, so focus on story and dialogue rather than impressive views and fight scenes. Keep the number of characters you have at a minimum, as you are likely to have a limited number of actors, and using the same actor for multiple characters may make your amateur film look too amateurish.
Make a list of locations in which you will film, and work out a schedule of when you will film your scenes. A well-thought-out plan will help you better direct your actors with minimal confusion and wasted time.
Select the actors for your film. You may be able to find people online willing to work cheap or for free. Organize an audition and invite them to come on a certain day to see if they fit your film. Be up front with them on how much -- or if -- you are able to pay them so you are not wasting their time.
Shoot your scenes. Try to get as many shots in as possible during the shooting period to minimize the time required. Shoot from several angles so you won't have to come back later and reshoot the scene when you get a different inspiration. Explain clearly to the actors exactly what kind of scene you are going for so you are all on the same page.
Edit the film using some professional video-editing software, which will help speed up the process. Start cutting out scenes to make the film a reasonable length. Choose whether you want a fade effect -- best between scenes -- or a straight cut -- best during a scene. Add a soundtrack as well if you want some music to spruce up your production.
Reserve an auditorium and a projector and host your premier. Invite the actors, friends, family, the public or whoever else you want to see your new film for the first time.