Step 1
Lenghten the skirt to ankles, then create the built-in collar on back by raising 2cm from back neckline and adding 1cm toward center back.
Draw back cutout from waistline, 5 to 10cm above it, ending at side seam with a gap 2 to 4cm wide.
Then draw a slash line slanted downward from center back to side seam passing through dart bottom apex.