Pre-smocked fabric is fabric that has been gathered in with the use of elastic thread. This is usually done using a smocking machine called a pleater. Usually, the smocking is applied to the top quarter of the fabric so that you can make a dress that is tight at the bodice and loose at the hem. Buying pre-smocked fabric is particularly useful because it saves you the time and trouble of either smocking the fabric or attaching elastic to the fabric.
Measure your bodice at the top of your bust using the tape measure.
Subtract 2-inches from that measurement.
Lay the fabric on a table or other flat surface.
Make a mark on the fabric along the top edge of the smocking side of the fabric, the measurement from Step 2 away from the fabric edge.
Sew the fabric across the width of the fabric in a straight vertical line using the machine straight stitch.
Cut the fabric 1/2-inch outside the stitch line.
Fold the piece of fabric in half, right sides together, matching up the side seams or edges of the fabric.
Sew the fabric using either a machine straight stitch or a serger along the fabric edge 5/8-inch from the fabric edge.
Put the dress on and make a mark along the length of the dress where you'd like it to finish.
Take the dress off and lay it flat on a table.
Cut the hem parallel to the bodice of the dress, 1-inch longer than the dot that you made.
Fold the hem back 1-inch.
Sew the hem, 3/4-inch from the fold edge using a machine straight stitch.
Turn the dress right-side out.