Outline an idea for your movie. You don't need to write a script, but at least put a general direction down on paper. Having an outline will help you focus your story and save you time when you begin shooting the movie. You should also meet with your actors and give them a copy of the outline. If you plan to let your actors improvise their dialogue based on your outline, the outline is all they will need, but if you want specific dialogue, consider writing at least a minimal script for your actors to memorize.
Shoot your movie using techniques and situations that will help you keep costs down. Avoid shooting night scenes where you will need a lot of extra lighting. Try to shoot all of each actor's scenes together when you can, so you don't find yourself having to contact an actor over and over. It doesn't matter if the scenes are out of sequence. You can fix that during the editing process. Even if you don't have a script, write the day's shooting schedule out the night before. This will help keep the filming process in motion. Keep your locations to a minimum. The less traveling you're required to do to shoot the movie, the less expense you will incur.
Use video editing software to put your raw footage together. The editing process can make or break your home movie, so don't be afraid to spend money on good software. Adobe Premiere is professional quality editing and effects software. Corel Video Studio and Cyberlink Power Director are also good choices. The software you choose is what you will use to arrange the scenes in your movie into a cohesive, smooth-flowing film. If you try to go too cheap with this software, you won't have the tools you need to accomplish your goals.