Balance the Side Seams

Lay one piece flat with marks up.

Lay the other piece on top with marks down, matching side seams.

Align the top corners of the side seams.

Place a pin at the point where the side seam straightens. Pin through both layers, but only catch a few threads of the fabric. You want to be able to pivot the top piece. (the location of this pivot point is different depending on the shape of the side seam).

Pivot the top piece until the grainlines line up (CB and CF are parallel, but they will not be lined up with one another).

Note that the crossgrain lines are also parallel.

Lift the corner where the hem and side seam intersect and look at how the two corners relate to one another.

Measure and mark the point halfway between the two seams.

Redraw both seams to meet this mark.

The side seam of the center front piece has been angled in more, narrowing this piece. The side seam of the center back piece has been angled out an equivalent amount, making this piece wider. (The net result of this shift is no change in the total circumference of the skirt) (Note that the angles of the crossgrain lines to the side seams are equal).