Mine turned out pretty 80's looking.
Here are the steps:
1. Cut the sides of the sweater, the neck off, and cut the sleeves off.
2. This is going to be the leg-warmer. While the sleeve is still folded in half, cut off the edge. Use the entire sleeve length, and I made mine the width of my calve so it would fit snuggly. The finished sleeve end will be the top, the unfinished edge will be near the foot. Repeat with other sleeve.
3. This will be the mini-dress. Cut the sweater body to fit your body type. I made my dress very fitted. I measured the top of my bust, under the bust, my waist, and hips. Divide these measurements in half to cut both pieces at once. (Or you could trace a dress that already fits and cut around it.)
4. Sew up the sides of the dress. I made sure my stripes lined up.
5. Sew the legwarmers up the one side, creating a tube.
6. Sew along the top hem of the dress, but leave one inch unhemmed. Measure elastic over your bust and cut accordingly. Attach a safety pin to one end of the elastic. (My elastic was from an old fitted sheet.) Feed the safety pin end through the hole, and pull through the entire casing you created. Once it reaches the end, sew the two ends of the elastic together. Hem the hole closed.
7. Tada! Match with accessories and leggings!