I am trial and error all the way.
When I have something I want in my head, I just go for it, no pattern all willy nilly style.
Sometimes it works out, sometimes it doesn't.
Round one was one of the former times, but round two worked out swimmingly.
Step 1: What You'll Need...
Then just a dress that fits well to use as a pattern (if you are not using stretchy fabric, then do not use a stretchy dress unless you cut it extra big; the first time, cut to size, the second time I about 1 1/2 timed the size).
I wanted cap sleeves, so I used a cap sleeve tee to get the pattern for that.