First, the physics. Get your weight back. If you can slide back in the seat it will help equalize the balance and lessen the load on the front end somewhat. Additionally, moving rearward can help you avoid putting as much weight on the bars, which will help you feel more in control.
Grip the tank with your legs. Using your thighs to grasp the tank will lock you onto the bike and keep your weight from shifting forward. It will also remove some weight from your wrists, which may make control manipulation easier. Gripping the tank will help prevent the feeling of "falling down" the hill into the curves, and will make you much more comfortable if you have to brake into a downhill corner.
Remember to keep your gaze up so you look as far ahead as possible. "Opening up" your field of vision is always a good idea, but it's that much easier to find yourself looking down and just ahead of your front wheel when your body is already aimed downhill. This will make everything seem as if it's rushing at you and can lead to target fixation. When looking downhill remember to also look well down the road.
Set your corner speed early. Again, this is a good general riding rule that reaps huge benefits in downhill situations. Keep in mind that you have to deal with the added forward weight bias caused by the slope. If you do your braking late or hold off getting your corner speed set until you're already in a downhill corner, you risk overloading the traction limit of the front tire when you ask it to handle the combined forces of gravity, braking and turning.
Use positive throttle control. You don't want to be on trailing throttle in a downhill corner, as this will tend to put a very high load on the front tire. If you've set your entry speed early and properly, you should be able to get back into the throttleeven if it's just a bitto shift the weight back with acceleration and balance things out. Just remember that with gravity pulling you along, a little throttle will go a long way.