All you need to know is how to use a sewing machine to straight-stitch and zig-zag... I'll explain everything else in detail!
I've got a few up for sale on Etsy... or you can just look at them as examples.
Step 1: Deciding on Size
Now, how long do you want your skirt? If you want it SHORTER than 30" long, take your hip size and divide by three. Round up to an integer. That is about how many ties you'll need for the body of the skirt. If you want it LONGER than 30", take your hip size and divide by two. Round up to an integer. That is about how many ties you'll need for the body of the skirt.
Step 2: Gathering Your Supplies
It's good to have a few extra ties. I recommend using only 100% silk or silk blend ties for them to hang the best.
You will also need:
iron and ironing board
presscloth (a scrap of cotton fabric will work)
source of electricity
water spritzer (filled with water)
tape measure (hopefully you've still got the one you measured your waist with)
ruler or straightedge
good sewing scissors
1/2" or 3/4" non-roll elastic a few inches longer than your waist size
all-purpose thread in the dominant color of the skirt (if your colors are schizophrenic, just use black or white)
non-bulky seam reinforcing tape/web (not shown in this picture, sorry!)