Take the sweater and measure it against your body, to get an idea of how long it is. if it's below the knee, cut to a length suitable to you and suitable to be a dress. Then roll the raw edge up twice, before sewing. Take a waist or hip belt (a unique take on a 20's dress) and clinch it round, so the jumper has a lovely, slouched drape. And there you have it, a sweater dress in half an hour!