Documentary Conventions

Archival Footage and Photographs
Archival materials include old photographs, newsreel footage, and even shots from fiction films. For example, The Atomic Cafe makes exclusive use of archival footage from the 1940s and 1950s to spoof American's Cold War fear of an atomic bomb.
Talking Heads
Talking heads are people interviewed to explain or comment on the text's subject. These people usually are shown in their offices (sometimes with a wall of books behind them) or in their homes.
Handheld Camera
A wobbly camera is often attributed to documentary. As cameras became more portable and more affordable, filmmakers did more on-location shooting, and keeping the camera steady was somewhat difficult when it came to following the action. Steadicam, a camera stabilizing system, aids in correcting what some perceive as a problem. The fiction film The Blair Witch Project makes use of the jiggly camera as a means of reinforcing its documentary-like style.
Voiceover Narration
Voiceover narration occurs when a voice is heard on the soundtrack without a matching source in the image. In other words we hear the voice speak but we cannot see the speaker utter the words. The voice often explains or comments on the visuals. Early documentary made extensive use of this convention, including Pare Lorentz's When the Plow Broke the Plains and The River.
Re-enactments
A re-enactment stages real events that already have occurred. Sometimes they include the people who experienced the events orginally, but more often they incorporate actors playing parts. Most documentary filmmakers shoot events where they actually occur.
Real People
For the most part, the people we see in a documentary are real people.

Sorce: http://www.documentarysite.com/study/documentaryconventions.html

Documentary Research

Weird Weekends:
Louis Theroux's Weird Weekends is a television documentary series, in which Louis Theroux gives viewers the chance to get brief glimpses into the worlds of individuals and groups that they would not normally come into contact with or experience up close. In most cases this means interviewing people with extreme beliefs of some kind, or just generally belonging to subcultures not known to exist by most or just frowned upon.

Survivalist:
In Idaho, Louis meets military enthusiasts and right-wing patriots who are preparing for a global catastrophe, including trips to survivalists' store Safetrek and a mountain refuge for conspiracy theorists called Almost Heaven. Louis also visits the Aryan Nation Church and helps to build a straw-bale home. The episode focuses on the survivalism movement and communities formed around it. The fact that several self-proclaimed survivalists were also hippies and environmentalists is a recurring theme.