I arranged the rectangle on myself so that the neckline was in the position I liked. Then I pinned one side. This way I found the center of the dress.
I found the center of one side of each sleeve and placed it to the center marks of the dress. I sewed them on (always the right side to the right side).
Here you can see the state the dress is in at the moment. The sleeves are a bit flared. They'll probably have a cord to tie them when it's cold.
Now I have to pay a visit to my victim to see if the thing suits and to mark the length of the sleeves and the place to insert the gores. The front and the back gore - I always have trouble with these. I know how to attach a gore to a seam, but at a blank piece of fabric I'm helpless all the time.. :-(
Maybe I should make one petty like this for poor me as well:-D