Sometimes, the easiest way to prepare for an evening out is to take a moment behind closed doors, slip out of your blouse or tee shirt, and button your cardigan (not quite all the way up!) over bare skin. If your cardigan is lightweight, not at ALL scratchy, and buttons up far enough for you to be comfortable, it's a great option to consider wearing it on it's own. Add more festive footwear, and some beautiful jewelry, push up your sleeves a bit, and smile!
Even if you are a VERY casual person, sparkly shoes and a serious necklace will elevate your jeans to an evening-appropriate ensemble.