4. Don't Whisper or Shout
If your video involves different scenes, such as you addressing the camera before cutting to a screencast, then ensure the volume levels of your voice are matched throughout. Most video editors offer a tool called volume normalization, which will do this, although you can look at the waveform view in most modern video editors to judge the volume levels by sight.
This might sound obvious but on many videos I've had to adjust the volume of my computer's speakers to keep up with what's being said.
Ensure that any opening or closing music is matched in with the speech volume too. As a rule, music that's a little quieter than speech is more acceptable than the other way around.
5. Edit, edit, edit
with doing everything in a single, long take. If you're an auteur filmmaker then this is forgivable, but splitting everything into smaller scenes and then editing it together later on will allow for an infinitely more professional final product. Remember that television has trained us to accept and even expect cuts during footage. One long take might seem like a more natural concept when you're recording, but the truth is anything but.
If you insist on going for a single take, at least allow yourself the freedom to edit later on. Listening to the take and chopping out any boring bits could help enormously. Ensure you shoot extra footage, such as close-ups or incidental shots, that you can use to cover up any edits. If you're recording an interview with somebody be sure to record ‘noddies'--footage of the interviewer nodding as if they're responding to what's being said. You can then paste these visuals over any cuts you make to the interview.
In Video: New Flip MinoHD Pocket Camcorder Has Solid Improvements
6. Light It Right
Bad lighting during a video recording is perhaps the worst sin of all. Apart from making any human subject look shifty, or simply less healthy, it can also cause the camera to lose its focus.
One simple solution is to move the computer or camera to just in front of a window, and recording during daylight. Daylight provides a diffused and encompassing source of light. Be careful if filming on a cloudy day, though, when light levels might rise and fall as the sun disappears.
If you have to use artificial lighting, learn about the principles of key lighting. This involves at one main light source illuminating the subject, supported by one or two other sources of light to fill in the shadows. These can be something as simple as desk lamps. Never, ever rely on a single source of artificial light for your video, unless it's extremely bright and you can bounce it off a wall in front of you so that the subject is covered in a diffused reflected light.
Keir Thomas has been writing about computing since the last century, and more recently has written several best-selling books. You can learn more about him at http://keirthomas.com.