This is a little project I've been wanting to do ever since my Alice in Wonderland Halloween costume. Completely original design. :) Although, I did use a pattern. It's New Look 6480 Junior Special Occasion Separates. Here's a few tips that I did differently from the original pattern:
-Metal boning is a MUST. I've found that corsets with plastic boning buckle way too easily. The first corset I made was with plastic boning, and within a couple of uses, the boning was a squiggly mess that I had to remove. The type of boning I prefer to use is weaved metal wire - I've found it's flexible enough to be comfortable, but it won't buckle like plastic. It's also less likely to break eventually with lots of wear, like regular metal boning. I've also found it easiest to sew together all the front panels of the corset, and measure how long you would need each piece of boning to be, while subtracting 5/8" seam allowance from each end of the panels.
-I added in the lacing on the back, just because I love how beautiful it looks. My personal preference is to make the corset 1 or 2 sizes smaller, so it allows for extra room to tighten the laces. However, I also kept the zipper in the design, for ease of use.