Draw the curved lines from the hip to the hem and the one from the shoulder to the hem.

On these lines there will be the gathering.

Draw the slash lines from the darts tip to the new lines to manipulate darts later.

Cut through the lines, get the separate pieces and close the darts opening the volume in the slash lines you created.

Draw parallel slash lines in all the three pieces to open the volume to be gathered.

Draft the collar: get the back and flip it over the front to draw the neckline, then mirror it to the other side.

Space the piece from the slash lines you created, add the volume and redraw the piece.

Repeat for the left front.

And for the ruffle.

Add a sleeve and the pattern is finished!