1. Cut fabric
Cut a piece of fabric about 44"x28” (112 x 70 cm). If your fabric is 44” (112 cm) wide, you will need about 3/4 yard (3/4 meter) per sling. If your fabric is 56-60" (142-152 cm) wide, you can cut the fabric in half parallel to the selvage edge and make two slings out of 1 1/3 yards (1.2 m) of fabric.
2. Hem the long edges
Hem the two long (44" / 112 cm) edges of the fabric rectangle. Lay fabric wrong side up on an ironing board. Turn edge over 1/4" (0.6 cm) and press.
Turn over again about 3/8" (1 cm) and press.
Stitch close to the inside edge of the hem.
3. Press a center line
Put the wrong sides together with the hemmed edges matching up. Iron the center fold line on each side.
4. Press the folds
Open up the fabric so the wrong side is facing up.
Take one of the hemmed edges and fold it up to meet the center fold line. Press.
Repeat a second time, folding the outside edge into the center. Press.
Repeat a third time. Press.
Do this with the other side, so that you have matching folds meeting in the center.
5. Tape the folds
Put masking tape about 1/4" (0.6 cm) from the raw edge. This holds the folds together. Put another piece of masking tape 5" (13 cm) from the raw edge, wrapping this piece all the way around the back. If necessary, trim the raw edge so it is nice and straight.
Now repeat steps 4 & 5 on the other side of the rectangle so each end has pleated folds.
6. Change sewing needles, if necessary.
I usually sew normal weight fabrics with either an 80/12 or 90/14 needle. For this next part, you'll probably want to switch up to a jean/denim weight needle (100/16).
7. Satin stitch raw edges
Do a satin stitch (a zig-zag stitch very close together) along the two raw folded edges. This makes the edge look nice and also keep threads from fraying. Pull out any loose fabric threads and trim.
8. Remove masking tape near satin stitching.
Keep other masking tape in place for now.
9. Put ring on.
Put the ring on the end of the fabric and fold the fabric over until the edge meets the masking tape. Be sure to fold so that the smooth (unfolded) side wraps over the ring.
Using a normal straight stitch, sew right along the edge of the satin stitch.
11. 2nd line of stitching.
Stitch a parallel line about 3/8" (1 cm) from the first line.
12. Decorative stitch (optional)
You can apply a third row of decorative stitches between the 2 lines of stitches.
13. Remove masking tape.
This picture shows the inside of the sling (you don't see the folds on the outside).
Put the other ring on the other side, and then you're done!