I tend to use sweet cider for mulling as it needs sweetening anyway but it does also work with dry.
In a saucepan: Varies to taste quite flexibly but roughly add between an eighth to a quarter pint of brandy and a quarter pint of water to a pint of cider, add 3-4 tablespoons of dark brown sugar and 1-2 sachets of mulled wine spice that they sell in supermarkets. Then bring the pan to just below boiling and hold at that temperature for roughly ten minutes. Pour into heat resistant drinking vessels and enjoy as it starts to reach your toes.