The key to any video/film is the writing. This is the skeleton on which all the visuals and audio hands. The best visuals can only be watched for so long.
Even if you are doing a documentary there is always editing and refining of the content of what is said. If you are creating a story from scratch then all the more reason to make the script the key to the piece. The beginning and end of the piece is the hardest to make work. You want to grab the audience at the beginning and you want to conclude the piece making sure your point/message has been made. The audience can forgive if the middle rabbles a bit so long as the end is strong. In a documentary you can pre-write an outline of what you want to cover making sure you get most of the content during filming. Then be flexible enough to alter what you capture to still make your point is made.
So make sure you take the time make the story work well.