Grouse have delicate skin, tears easily. I don't even try to pluck them.
Lay the grouse on it's back on the ground, put your feet on each side on top of the outstretched wings (close to the body), grasp both feet and pull up with steady pressure. The bird will seperate and you'll have the legs with guts attached in your hands, leaving the breast and wings on the ground. Cut the wings off the breast.
To cook, I usually just slice the breast meat off the bone (like carving a turkey) in fairly thin slices. Roll in flour, pepper to taste, fry in butter or your choice of oil (HOT), just long enough to brown both sides and it's done. Real quick and easy and the meat doesn't dry out like when you try to roast it without the skin on.
Best way I've found to dry pick ducks is to hold the bird by the neck, grasp some feathers between your thumb and forefinger, and while sort of rolling your thumb in towards the skin you pull downward towards the tail end of the bird. Just pull off a small amount of feathers at a time and keep working from the neck towards the tail.