How to make Prime Rib for Beginners. Use this formula for cook time. For every pound multiply by 5 and cook at 500f degrees then turn off heat and leave in oven for 2 hours. Step one - salt the prime rib and place uncovered in the refrigerator overnight. Step two - take out of the refrigerator for 2 hours and pat dry with a paper towel. Step three - trim some of the fat on top. Step four - tie tightly with kitchen twine. Step five - season generously and place on cooking rack. Step six - preheat