Be sure you take the lens cap off the lens. :thumbup:
If you are using a Nikon camera, turn on the Active D-Lighting feature and set it as high as it will go, since it will be mid day and cowboys wear wide brimmed hats. (Note: it will slow down your buffer)
Set the shooting mode to Aperture Priority.
Set the ISO to it's lowest native value.
Set the exposure meter to Center-Weighted.
Set the shutter release to burst mode.
Set the autofocus to Continuous. (Note: keep an eye on/listen for the beep of the in-focus indicator in the viewfinder.)
Set Focus to the back focus button.
If possible, shoot from a low perspective to minimize busy backgrounds and to add power and stature to the riders and the animals.
Faces and expressions, framed by blurred backgrounds, are the holy grail of action sports shooting.
Shooting action sports is one of the more difficult kinds of photography to shoot.