1. Procure the skirt.
This works best if you don’t select the skirt yourself. It’s preferable that the skirt be given to you by someone to whom you cannot say no without risk of offense, like an over-sensitive and/or passive aggressive mother-in-law.
The skirt should be in a color that you do not like, that matches nothing in your fabric stash, and even more important, does not coordinate with any thread you already own. (Note that the color must be ugly enough that you will refuse to buy matching thread because you know that you will never ever use it again.)
Ideally, the skirt will be sewn of various small pieces of fabric, preferably cut on the bias, to create a patchwork effect. This, together with an asymmetrical hem, will ensure that it is nearly impossible to cut pieces for a garment that will fit anyone larger than an infant.
The skirt should be in a fabric that is difficult to work with: something as simple as a loosely-woven linen blend that shifts whenever you try to cut it will suffice.
Lastly, it should have a large embroidered motif that must be incorporated into the new design, lest offense be given to the giver of the skirt. (This is why the first tip is of such great importance.) The motif should be set off center in its patchwork piece, and close to a side seam, such that it becomes impossible to incorporate it into the new design in any coherent way.
2. Remove the zipper and lose it.
3. Pick a pattern that requires you to do something 1) that you have never done before, (in my case, piping) and 2) that you are not good at doing (perhaps buttonholes, just one example.) Your dress will be particularly ugly if you pick a pattern that requires the use of coordinating fabric, as you have none.
4. Work on the dress while you wait for an item required to finish another project, i.e. the project that you really want to be working on. This will ensure that you give the correct amount and type of attention given to the ugly dress project, such that the dress will be sufficiently ugly.
If you follow these instructions, you could wind up with something that looks like this:
And there you have it, the ugly dress, suitable for wearing whenever one expects to paint, or to draw with felt-tip pens, to play in the dirt, etc. It may be ugly, but it is a valuable and reliable pinch-hitter that keeps the nice dresses (the ones you wanted to make) from being ruined too quickly.