Use a measuring tape to determine the size and width of the rocking chair's seat. If you are not good at taking direct measurements, simply place newsprint or butcher paper onto the seat, trace the seat and then measure the trace in order to determine the required dimensions. Make sure that you add 2 inches to all the measurements that you take in order to compensate the piece of fabric which will be consumed up while you sew the cushions.
Now it is time to cut the fabric according to the measurements from the earlier step. Lay the piece of fabric and fold it such that the printed sides face inwards. Cut out a piece of fabric in desired shape according to the size and width of the seat. You will have to use a pair of scissors for this purpose.
For the ruffles, you will be required three strips of 8-inches wide fabric. The length of these pieces should be 1.5 times the length of front and sides. For instance, if the front of the chair measures 20 inches in length, the front ruffle strip has to be 20 × 1.5 = 30 inches.
Keeping the right side of the strips to right side, fold them up in half and iron them until they are flat. Sew the strips so that they close along the short sides. After you are done sewing the strips, simply rotate them right side out. Again press them flat with a hot iron.
Along the open side of one of the strips, sew a line of basting stitches. Make sure that you sew the line fairly loose. Anchor the sewing thread at one of the ends by tying that end in a knot. Hold the anchored end with one hand and slide the fabric with the other hand along the line of basting stitches. The piece of strips will gather in the shape of a ruffle. Repeat the same method for other two strips and gather them into ruffles as well.
Take a piece of seat fabric that you cut in Step 2 and place it on a flat surface, keeping the printed side of the fabric up. Lay the front and the side ruffles such that the basted sides of the ruffles match up with the fabric's edge. Also, the ruffling should be centred in towards the fabric.
Make adjustments to the ruffles until they fit properly in place. Pin them to the piece of seat fabric.
Slash four pieces of grosgrain ribbon. The length of piece of ribbon should be 12 inches. Fold all four pieces in half and use straight pins to secure the folded ends of the ribbon pieces to the four corners of the seat fabric. Trail the loose corners of the grosgrain ribbon towards the centre of the fabric.
Pin up the second piece of seat fabric after placing it exactly on top of the first piece of seat fabric and matching the edges. Stitch together the two pieces of seat fabric, leaving out the inner ruffle and ribbon ends.
After you are done stitching fill the hollow space in the cushion with poly fibrefill. Finally, sew the open end of the cushion.