It is challenging yet a rewarding career to produce documentary films. There are those documentary filmmakers who are found of letting the talking heads play a major role. This is done with the talking heads being interviewed with an artistic backdrop. This type of documentary is simply boring to watch. If the subject of the documentary would just be talking about their personal experiences, then it would be better to come up with a printed material than a documentary film. More info can be found below so be sure to check it out!

Always keep it in mind that making documentary films means showing them the subject and not telling. You have to show them what violence is instead of telling them. You have to consider your audience to be intelligent and able to come up with their own meanings and conclusions. You can start by filming your immediate neighborhood which is considered as the cradle of criminality. You can show the way people live, their routine, their work, and what they do during their free time, etc.

You have to realize that a documentary is a visual medium. That's why you have to make sure that your audience's visual senses are catered to. It is not visually entertaining to watch a person speak. It can be interesting to hear or read; hence the audio book or the traditional printed book would do well for it. But when it comes to a documentary, it should be pleasant to the eyes. 

You can't however remove all the talking heads all the way. They can be used for explanation complicated subjects, provide background information for some information gaps that have to be filled in, and they can also give validation to your film's hypothesis. The trick is to use them sparingly. 
You should also keep in mind that producing documentary films doesn't require the use of actors and made-up sets. What you can see are real people thriving and getting on with their lives while you are there filming them. 

That's why documentaries are known in the entire world's history as having strong and deep impact on cultural meanings. That's why film schools around the world include documentary filmmaking in their offerings. In these schools, classes teach the basic aesthetic tools used for documentary filmmaking such as camera usage and operation, lighting, structure, and sound. Classes will be geared towards producing and directing documentary films.  

You have to remember that documentaries always stir up controversies. It all started with the "actuality films" that the Lumiere brothers created. Visit this link to know more.