Mistakes Still Photographers Make When Shooting Video With a DSLR

They don’t understand the importance of audio and don’t use external microphones. Audio is everything in video.
They think in “moments in time” and start shooting video too late or stop shooting too soon. You need to let the camera linger longer.
They don’t shoot sequences with a beginning, middle and end.
They don’t think in “storyboard mode” – You should ask yourself “How will I get into and out of a shot and what’s next in the story?”
They don’t shoot enough B-roll with variations in angles and focal lengths – very important in the editing process.
They move the camera instead of letting the motion take place in front of the camera.
They turn the camera vertically. There aren’t too many vertical TV sets and monitors.
They don’t use a tripod forgetting that video is “time in motion”. It’s one thing to hold a camera steady for 1/60^th of a second and quite another to hold the shot steady for 10 seconds.
They don’t consider the frame rate and how that will affect workflow and editing.
Aren’t careful keeping their sensors clean from dust. Retouching video is a lot more involved than spotting still images.
They “throw” some video clips in with the still photography job, not putting an added value on them and thus setting a bad precedent with clients.
They don’t consider the output and the type of file to be delivered. There are dozens of formats and codecs in video. Choose according to your target audience and viewing platform or device.