Shoot in good lighting. Video needs lots of light. If it's too dark inside, then go out, at least for your first project or two. Use a big memory card. Video takes up much more memory than still pictures. I recommend 1GB. Record at the highest quality and resolution possible. For example, if you camera supports 640x480 at 30fps, go for it. Get close. Compose your frame tightly. These movies will be viewed at 320x240, which isn't exactly movie theater size. So stay away from distance shots and get close to your subjects. Try to avoid too much background noise (audio). On-camera microphones tend to pick up *everything,* so try to control background noise best you can. And beware of wind! It sounds terrible. Figure out what you're going to shoot before you press the record button. You don't have to have a full blown storyboard, but sketch out your scenes beforehand. Keep your movies to 5 minutes or less. You have a better chance of holding your audience's attention.
Some great tips if you are getting started in vodcasting.