Keep it on for 10 to 20 seconds each time. Make sure the date and time are set correctly. Watch out for time zone changes as well as daylight savings time. During playback through the camera, the invisible time code can be displayed. Pause for a few seconds after you have started your video.
Many older cameras record a few seconds of color swipe at the beginning of a segment.
Stay close to the camera during narration. Some radio transmissions will effect your video with RF-noise. This is especially true if you are standing next to the antenna. Try to limit radio transmissions during good times, especially if there are other spotters in other vehicles transmitting redundant storm information. Try moving away from the vehicle's antenna.