There are a couple of things I’ve noticed in working along side people that do video on the side or even for corporate/educational events:

First, don’t mix types of camera.
This is generally not a good idea. It’s one thing to have a two models of consumer camera from the same manufacturer; it’s another to mix a prosumer camera with a consumer one. Consumer cameras generally only have one image processing chip (ccd), so colors are much less vivid than in prosumer cameras which generally have three. Even in consumer cameras with three chips, the chips are smaller and thus capture less light than their larger cousins. The difference will be noticeable.

Your built-in mic is probably not good enough.
Have you ever watched a tape someone shot with their camcorder and were distracted by the bad sound? Most of the time that’s because amateurs tend to use the built-in mic. There are times when this can work out (close up, in a quiet room, when you have no other choice), but unless it’s a shotgun mic (which will likely only be standard on high end prosumer and professional cameras), you’re not likely to like the result. These mics tend to be omni-directional, picking up sound from all directions equally, instead of just what’s straight ahead. Additionally, internal mics pick up sounds like the sounds of the camera’s tape transport mechanism and any sound from the operator. Combine that with the auto-gain “feature” that most cameras have and you’ve got loud noises and amplified background sound.

Avoid mixing HD and SD cams. Just like the first mistake, if you’re editing HD and SD footage together, you’ve got some issues to overcome. Standard definition video is 480i. That means there are 480 lines of horizontal resolution that are drawn starting with numbers 1, 3, 5, etc. and then drawn 2, 4, 6, etc. HD cams record 720p (720 horizontal lines, drawn 1, 2, 3, 4, 5, 6, etc.), 1080i (1080 lines, drawn 1, 3, 5, etc, 2, 4, 6, etc.) or 1080p (1080 lines, drawn 1, 2, 3, 4, 5, 6, etc.). Mixing SD and HD footage at HD resolutions will result in either a smaller picture (by comparison) or a stretched fuzzy (or pixelated, depending on the display) picture. Mixing SD and HD footage in SD results in either a cropped or shrunken HD image.

If possible, use a tripod or other type of camera support.
I don’t care how steady you think your hand is, unless you’re really close (I’m talking a few inches to a few feet) and resting the camera on something, you’ll always be shaking the cameral some.

Good for viewing isn’t good for editing.
It used to be the case that people had camcorders that took full-size vhs tapes. This meant viewing footage was easy. Just take out the tape and stick it in your home vcr. VHS-C had similar advantages, but at a cost to resolution.

I remember my wife looking for an adapter to play an 8mm tape in a vcr. These analog tapes were similar, but not similar enough to enable playback in a vhs vcr. The advantage of 8mm tapes was better in many ways.

Now, mini-dv is the de facto standard. It is used to record both SD video and HD video using HDV to record higher resolutions. Either can be edited without much trouble although HDV cameras is a more difficult format to use. Whether it’s mini-DVDs or some of the new HD formats, editing is more challenging. Avoid them if you can.

Ambient light doesn’t work.
God is much better at making cameras (although we call His cameras, “eyes”) than we are. As such, the amount of light necessary for you to see is much less than what cameras need to “see”. This is why television studios are brightly lit. Night shots are usually day shots darkened in editing to look like night. In fact, there’s little that’s “natural” about video lighting. If it looks natural to your eye it probably won’t look good to the camera. If it looks odd, it still might look bad on camera, but you’re probably closer to doing it right.

Video takes much more time than you think.
From set up, to taping multiple takes to editing. Unless it’s “live to tape” (and all the equipment stays set up when not in use), video takes hours and hours longer than the finished product to produce. I used to hear that for every finished minute of video it takes 1 hour of editing. That can easily stretch into 12 hours, or days and days. A movie doesn’t take a mere 120 hours to edit. It’s likely more like months to complete. Short projects might only take a few hours, but (with the exception of tv news packages which are “quick and dirty”) even a piece that will play for 2 minutes will likely take several hours to produce.

Automatic features are bad.
As you progress in you shooting skills, you should use fewer and fewer automatic features on your camera. Auto-iris often gets confused, correcting exposure for light or dark clothing instead of flesh tones. Auto focus might choose to make the background sharper than the actual subject of your shot. These are tools to get you into the right ball park of what you want, but not hit a pitch out of it. For truly creative and interesting shots, you’re going to have to constantly think about focus, iris, shutter speed, sound levels, white balance, etc.

Less experience = less camera movement.
At least that should be the way it is. People new to or untrained in camera work often quickly move from shot to shot zooming in a nausea-inducing manner. Watch some older movies and most television shows made before the 1990’s and you’ll have a difficult time finding quick zooms or pans. In newer shows, quick movements are more common, but they’re also more difficult to get right, so that they remind the viewer of his/her own head movements and not a ride on the tilt-a-whirl.