focal length
Zooming out to the widest possible mode of the camera will allow you to include more sky and more foreground in the image. If you’re using the kit lens that came with your camera, this means turning the zoom wheel to the smallest number, e.g., 18mm in a standard 18-55mm lens.
Longer focal length will help creating the star trails faster, as the narrower the field of view is, the faster the stars elongate into a smear instead of a dot. However, longer focal lengths allow for less sky and foreground in the image.