So, I had this skirt (well, a whole bunch, actually). They were too long, to big at the waist.. but nice, good quality fabric. This paticular one was from the posh-posh shop Hobbs, and was 100% linen. Not something I'd be able to afford.
Ok, so I put it on. Like a dress, I suppose, over your boobs. Pin it how you want on both sides, and then -carefully- take it off. Sew sew, leave zipper room.
Right, now measure your waist. If the soon-to-be-dress is muuch bigger around your waist, you'll want this step, if not, skip it. Or you could always wear a belt.
Take some ribbon, and attatch it around the waist of the dress, gathering the fabric every three inches or so.
Actually, I didn't do the waist, I did the under-boob part. Whichever you want.
Add straps, and, if you'd like, trim on the top and bottom. Sorted!