I did them for DD's school nativity and they are so easy. If you have fabric, cut it into lengths that are double the length of the skirt and then fold in half, in, in half etc until it is about 4". then cut strips off the folded fabric. I would go for about 3 inch strips so that when it is tied on, it gathers slightly. Then tie a few strips onto elastic. Can't remember how many I used in one tie, but fold in half, put behind the elastic and pull the tails through the loop. Don't pull then too tight as you will stretch the elastic. You can also tie in ribbons and other strips etc. For ours, we had white tulle with silver ribbon as the girls were snowflakes. Very effective.