Lab videography
Taking quality lab videos is not difficult. Most cell phone cameras with a video function will produce footage of sufficient quality to be uploaded for documentation. However, videos of length, which contain narration and instructions for the viewer, require more sophisticated editing.
Contents
Videography
The basic rules in the article Lab photography apply.
Narration
The most difficult part of narrating a video is keeping the narration in sync with the events in the video. Generally it is a good idea to narrate the video separately from the filming, so any mistakes can be edited out and the video length controlled more precisely.
Position
For a better view of the experiment, it's recommended that you record the experiment, while standing either behind or on a side of the camera.
Software
Audacity is good software for editing audio in narrations. It allows for multi-track editing and numerous effects on the audio, which can be used to improve sound quality.
For advanced video editing (usually zooming in, speeding up clips, adding FX) Vegas Pro or After Effects are a good bet (though they're not free). For simple video editing, Movie Maker is your best bet and it's free.