I've had goose for the last 3 or 4 Christmas' and love it. This is what I do: (for a 10-12lb goose - sorry don't do metric!)
Take out all loose fat and giblets. Wash and dry well, prick goose all over. Rub with salt and pepper. Into the cavity put 1 onion, quartered and 1 lemon, quartered. Put into a pre-heated oven, gas mark 7 for 15 minutes then lower heat to gas mark 4 and cook for 3 1/2 hours. You do have to drain off the fat a few times. If the goose is browning too soon cover with a piece of foil.