Short but to the point – common mistakes still photographers make when starting to shoot video:
1. They break timecode (only applies when shooting to tape)
2. Bad audio – audio is everything in video.
3. They don’t turn the camera on soon enough.
4. They turn the camera off too soon (thinking in the “decisive moment)
5. Use auto – focus.
6. They don’t shoot sequences – beginning, middle and end
7. They don’t shoot in “storyboard mode” – “How will I get into and out of a shot and what’s next?”
8. They pan and tilt and zoom in and out – too much – the motion should come from the subject matter – not necessarily the camera.
9. They don’t shoot enough B-roll with variations.
10. I’m open to suggestions as to what #10 should be – feel free to chime in.
Journeys of a Hybrid 
They turn the camera vertical! At least with pocket & point & shoot cameras with video.
– they try to hand-hold. unless you’re using a steady-cam rig of some sort, video should be shot on a tripod.
For the most part, I would agree with saying use a tripod – however with the right camera – for me it’s a camera that’s large enough to steady on my shoulder, shooting a fairly wide (angle) shot and getting close to the action – it’s doable without a glide cam or steady-cam. TV news guys do it all the time.
You have three chances to tell a story with video. When you:
A. Write it/Plan it (in the case of reportage)
B. Shoot it
C. Edit it.
Photographers seems to think the most important part is B, and forget that story (as always) is king.
My number 10 is they tend to zoom instead of walking into the shot (when hand-held). Zooming just adds to camera shake which isn’t a problem when shooting stills at a high shutter speed. With video it’s just shaky and ugly.
I would like to say a still photographer probably has more respect for the background and composition. I encourage all videographers I train to pick up and learn still photography.