Step 3: Cutting Off Extra Bits
Pin the sleeves together in the back and button up the buttons, so that the dress stays up. Then you'll have to fuss around a bit to make sure everything will fold right. You may need to tuck in little bits of fabric along the side, and tug out other bits so they don't get lumpy. These little adjustments don't have to be permanent yet - just make sure that you'll be able to get the front of the dress to look ok, and you can tack down the folds later if you need to.
You'll have to decide whether you want to keep the collar or not. If you don't want it, now's the time to cut it off.
Now you have to cut the sleeves short. Stretch the sleeves behind the person's back, and mark where to cut them. The ends must overlap by at least a few inches, so there's room for buttons and buttonholes and for hemming the ends.
If you started out with a short sleeved shirt, you probably won't have to cut the sleeves any shorter.