After you cool the beef stock overnight, put it in the fridge so that the oil would solidify on top and it'll be easy to skim the fat off later. See all that white fat, yuck!
After you skim the fat off, bring the stock to boil again, take the oxtails out, put them in a large bowl, then put some spinach or other greens on top, then some chopped spring onions and some salt. After you assemble the bowl, pour the boiling beef stock over everything, and tada, a bowl of delicious beef oxtail noodle soup. Oh, actually I forgot to get the noodles, oh well. And I forgot to take a pic of the final product. Oh well.