Stud the oranges with cloves. (Push the pointy end into them until the flower part is flush with the peel.) I use about 10 per orange. You may want to peel the top layer of skin off the orange if you don't want to ingest the dyes they put on them to make them orange. Put the cider into a large saucepan, and add the oranges and some cinnamon sticks (one or two will do). Heat for hours (you can just leave it on all day for a party). It gets better with age. Just pour in more cider when it starts getting low.
The best Hot Cider drink you've ever drank!