1. Using a pair of shorts (or pajama pants, in my case) as a pattern, cut 2 FRONT pieces and two BACK pieces for your shorts. Cut the sides to be slightly higher, and make sure to cut your BACK pieces longer so they completely cover your cheeks :) Also cut a WAISTBAND, 1 1/2 to 2 times the circumference of your waist and 3" tall.
2. Sew your two FRONT pieces together from waistband to crotch.
3. Repeat step 2 for your BACK pieces.
4. Put the FRONT and BACK pieces of your shorts together with right sides together.
5. With right sides together, sew the ends of your waistband together, forming a loop.
6. Fold the waistband in half so it's now 1 1/2 inches tall and has a folded edge on one side and two selvaged edges on the other side.
7. Pin the waistband of the fabric around the top of the shorts. Make sure the folded side of the waistband is facing down toward the bottom of the shorts, as marked in this step. Sew around the entire waistband with a straight stitch and a 1/2" seam allowance, but leave 3-4 inches open so you have a spot to slide your elastic inside.
8. Measure your natural waist and cut a piece of to this size. Attach a pin to one end and use it to feed the elastic through the waistband casing you just created. Make sure the other end of the elastic doesn't disappear into your casing -- secure it with a pin as it gets close. Once both ends of the elastic are sticking out of your casing and the elastic is completely fed through, sew the ends of the elastic together. I typically use a serged seam to securely sew them together, but you can use a straight stitch or a zigzag stitch.
9. With the waistband still folded down, like before, sew up the little opening in the casing. Fold your waistband up and press in place.
10. Hem the shorts to your desired length.
11. Cut the pom-pom trim to your desired length for each leg, then pin to the shorts hem and sew around the leg holes one more time, attaching the trim to the bottom of your shorts. And you're done!
FUENTE : Encontrado en merricksart.com