First, get the fabric. Its called "crushed velvet" and its found at most fabric/craft shops(especially during Halloween time). Make sure its stretchy, or else this project wont work! You can also find it easily on eBay. There are many many fun colors to choose from! I wanted mine to look leafish, so I bought dark green.
A yard should be plenty.
 

Take the fabric and wrap it around yourself as tight as it can go(the tighter the better because its what causes it to stay up!). Mark it with a pin or a safety pin.

From your mark, cut the fabric. 
 

Turn the fabric inside out. Thread a needle and sew the fabric together (or if you know how to use a sewing machine, use that of course!). From the top, you may want to sew it in about an inch smaller than your mark- just to ensure the tightness from the top. As you go down, flare outwards to help it fit the curves of your body. You might want to try it on a few times while sewing help make adjustments. Don't sew all the way down to the end. You might want to leave a slit that will be on the side of your thigh.

Now is the fun part! Tattering and cutting up the dress's edges. Make it jagged, asymmetrical, full of holes, anything you want! Try it on a few times while doing this, so you know how the end result will look.

Once you're all done, it should look something like this!  If you want to add extra embellishments, by all means do so! Get creative! You can use fabric glitter glue to make leaf veins going down the center (or off center!), you can sew on flowers or ivy leaf vines (fake ones will last longer). You can even add a lace trim or use a ribbon to lace the dress up down the side. ..the possibilities are endless.
 

Got any left over scraps? Why not try and cutting into a triangle shape and then sewing it together to make a Leaf top? You can pair it up with your dress for a nice layered effect, Or wear it with a cute skirt!