1. Pre-wash all your fabrics and iron.
2. Determine how wide you'd like the waistband to be and add half an inch for seam allowance. Measure the diameter of the shirt where you'd like to place the waistband. Add half an inch for seam allowance. Use these two measurements to cut two identical pieces of fabric.
3. Determine how long you'd like your skirt be. Double that number and add half an inch for seam allowance. The width will be double the width of your the waistband pieces. Use these two measurements to cut two identical pieces of fabric.
4. Fold your skirt pieces in half lengthwise with the wrong sides together and iron. This way you won't have to sew a hem on the bottom of your dress and your skirt will be double-sided. No ugly back side of the fabric will show no matter how much your little ballerina twirls.
(Not sure why this is sideways. I'll work on that.)
5. Put the two right sides of your waistband pieces together and sew one of the short sides. Do the same on your skirt pieces. Iron the seams open.
6. Pin the right side of your waist band fabric to your shirt so that the seam of the waistband lines up with one of the seams of your shirt and sew. Fold the waistband fabric down over the seam and iron the seams down.
7. Take your skirt fabric and baste all the way along the long open seam. Do not backstitch and leave your thread a bit long. Hold one piece of thread and gently pull the other piece of thread to gather the fabric.
8. Pin your skirt fabric to the right side of your waistband fabric so that the seams line up and adjust your gathering so that it is even. Carefully sew these two pieces together. Fold the skirt fabric down over the seam and iron the seams down.
9. Turn your dress inside out and sew the final seam together. Iron the seam open.
10. Embellish in any way you like.
Close up of my embellishment
I'm sure I didn't explain this well. So if you have any questions don't hesitate to ask and I'll do my best to clarify.