1 yard of knit
Step 1: Fold your material in half hot dog style.
Step 2: Stitch up the long side. (I used a long zig-zag because that was what I saw suggested for working with knits.)
Step 3: Fold down the top hem about an inch and sew, leaving a two inch opening for inserting the elastic.
Step 4: Thread elastic into the top opening, sew it to itself, stitch the hole the rest of the way.
Step 5: Use scissors to trip the bottom of the skirt to the correct length.
And that's it! This required two straight seams (along the side and the top hem), and the few short stitches when sewing the elastic to itself. This is the easiest project imaginable! It took me about ten minutes.
Now, the down side. Apparently knits aren't great at bunching. The extra fabric at the top--since I didn't measure my waist and trim accordingly--doesn't separate on its own. You need to manually get the gathered parts to spread out along the elastic. This isn't a big deal to me since I typically wear long shirts that don't show anywhere near the top waistband.
But, I got the job done in time to wear it to a performance that night. It all worked out in the end.
I case you can't tell, this is an outfit I've assembled for casual cosplay. It's fashioned after Chihiro from the Miyazaki anime "Spirited Away."