This is what the original skirt looked like.
Pin the skirt to create a silhouette you want.
Gather small bits and pieces of tulle together (or rip a piece out of a larger piece) and pin it onto the skirt.
Sew the tulle onto the skirt, and add more tulle.
Keep on adding more tulle- make sure that the volume is right, and add more tulle on areas that lack volume.
This is what the finished skirt looks like :D