Lighting
Most important factor. Make use of sunlight, which is the best. Extra lighting equipment can enhance your setup even further.
Audio
Some of the best performing ambassador videos have no music. It's subtle but bad audio quality can ruin an otherwise great video. Using a good mic is so important.
Camera Stability
Always film your videos using the back camera and use a tripod to position your phone. You can use a selfie monitor or a mirror so you can see yourself while filming.
Background
A clean backdrop keeps the focus on the products. Clutter or a messy environment will hurt your video's chances of going viral.