For prom dresses with only one skirt layer, I suggest you shorten the skirt on the dress and use the extra skirt material to make additional layers on the skirt.
For a long-lasting dress, follow this photo tutorial to shorten a skirt: How to Shorten a Skirt Otherwise, just chop the skirt without hemming.
To make additional skirt layers from the extra material, add a drawstring casing to each layer. To do this, simply fold over the top of the extra skirt fabric about 1" and sew all the way around to make a small tube. Leave a small hole in one part of the tube to add a drawstring. Ribbon makes a quick and cute drawstring.
Use the directions on how to add a ribbon drawstring: How to Replace a Drawstring
Once your additional layers have a drawstring, you can put them on over your dress skirt. Since the extra material from the bottom of the skirt is considerably wider than your waist, you have an instant poofy skirt once the extra layers are tied on.
I would not advise cutting the sleeves off of your dress unless you plan to trim the raw edges at your shoulders with fake leaves from the craft store, or are going for a tousled fairy look. Fake leaves are so cheap and easy to hot glue or stitch to any part of an outfit. Have fun at the craft store and find coordinating flowers to make wristbands, anklets or crowns out of. This looks very nice with fall colors.
You can also trim the bodice of your prom dress with matching leaves and flowers to complete the look, or cover it with an easy corset top.
I have also put together a photo tutorial on how to make fairy wings to match. There is the butterfly style for most fairies, and the dragon style for dark or bat-like fairies.
If you don't have a prom dress lying around, these are in great supply at any thrift store. Turn something hideous from the 80's into a fine fairy costume.
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