Plan your approach. Action movies involve every kind of physical exertion: you can have a film about killing, detective work, martial arts, road racing, motorcycle stunts and so on. Who do you have available to work with? What athletic skills do you and your group possess? These questions help you determine what kind of film you can make.
Script your dialogue and action sequences. Plan, either alone or in collaboration, everything that the characters say and do during the length of the film. Make sure that the script is clear, clean and well-rehearsed so that, when filming starts, there are as few snags as possible.
Practice fight and stunt scenes as many times as necessary before filming. Fight scenes require close coordination between participants. For example, to set up a punch, make sure that the puncher knows how fast to throw his punch, and in what direction. Make sure, as well, that the punchee knows exactly when to move the supposedly affected part of the body. A punch to the chin doesn't look convincing if the recipient of the punch moves his head too soon. If he moves it too late, the punch becomes real.
Be free and open with the possibilities. Action sequences sometimes run their own course, no matter what the script says. At times, you can see possibilities for the development of a scene only when you're there, on location, in the moment. Let the creative moment take control now and again.
Use any of the various types of video cameras that are on the market today, and become proficient with the video editing software that you may be able to buy with the camera. It's rare that a film can be shot without having the need to go through extensive editing, so be ready to work the film over as much as needed in order to make it presentable.
Accept the fact that you need to edit whatever you film. Plan to film scenes that use the same set as a group, one after the other, even if they don't chronologically follow one another in the script. Later, you can switch the order of scenes in your editing software.
Add titles and credits and other such lettering as needed, put some professional polish on the whole thing and get ready for your big debut. The sky's the limit and only your imagination can show you the path forward or hold you back.