Always film with your back to the sun. Make sure you keep the camera steady and try and keep the horse in the centre of the frame
Try not to film when there is a sharp contrast in light and dark areas in the arena.
Use the highest quality setting on your camera.
Set the zoom before you start and do not alter it once you have started filming.
Make sure the light setting is correct for the time of day you are filming at. Stand at C either with your back to C or behind C facing A and do not move from that spot.
Make sure you video from the start of the test as they turn onto the centre line and keep videoing until after the final halt so we can see some walk work as they leave
the arena. (Just half a dozen steps or so).
Film with the sound turned off if this is an option on the equipment you are using. This helps to keep the file size down.