I picked up this long velvet skirt (probably worn by a bridesmaid) a few years ago at goodwill. I suggest going this route as velvet can be super pricy and you'll save tons of money and time by doing things this way.
I marked how long I wanted my skirt to be, added a couple inches for a casing and cut the bottom of the skirt off.
It was here that I realized the skirt had in fact been hand made (and not very well for that matter) so I had to go back and do a lot of adjustments. Otherwise, this would have been done a lot faster.
The skirt wasn't originally crushed, but it was wrinkled and I decided to cover some of the mistakes from the original sewer I'd crush the velvet. This step is however optional.
If you do want to crush the velvet, set your iron on the silk setting. start bunching your skirt and press over the right side of the fabric. It's pretty time consuming though so no pressure to do this.
Note: This will only work on real velvet made of silk or rayon. This will not work on a polyester velvet.
When you've finished crushing the velvet it should look like this.
If you have any raw edges this is a good time to finish them off with either pinking shears or a serger.
Next sew a casing for the top of the skirt. Run elastic through your casing. Sew the two ends of your elastic together and sew up the casing. (the construction of this skirt is really easy right?)
If you ended up taking out the original hem, like I did, then sew it up at this point and you're done! Super easy right?