For the party, I made a skirt for my daughter to wear out of three different red fabrics: large polka dots, small polka dots, and stripes at the bottom.

First, I used another skirt that fits her to measure the elastic and pinned the elastic so I'd know where to sew it together.
Then I used my sewing machine to hem the ends of the first fabric, cut into a rectangle.  I just used a zig-zag stitch with very small width and movement to make it like a serged edge.  I like this method rather than hemming it by folding it because I never get the hem straight.
Here are my machine settings.  Extremely small stitch size and an extremely small width of zig-zag.
See, now that rectangle is hemmed on one side.
I didn't take a picture, but before this, I had made another, wider rectangle from the striped fabric, and sewed a pocket for the elastic to go on.  I didn't thread the elastic through until the end.  Next, I sewed the hemmed fabric onto the base fabric using a regular stitch.  I first sewed it right sides together, then as you can see in the picture below, I folded the fabric over and sewed along the top of the seam to keep the ruffle down.
I used this method for the next ruffle, in a different polkadot pattern for a second tier and sewed that on.  Next I took the elastic and marked where the pin was, then threaded it through the casing on the striped fabric.
After it is threaded all the way through, I sewed it together.
Note, this isn't the perfect way to make an elastic casing.  Since I had sewed the casing all the way to the fabric edge, I had no way to sew the casing shut cleanly after I threaded the elastic, without catching the elastic, so I just didn't.  The fabric was gathered way too much for anyone to notice. It was a big hit and looked quite cute.  Because I used a rectangle shape, the skirt had a pencil skirt shape and stayed down rather than flying up more like an A line or circle skirt. 
Happy Birthday Millie!