Here are three tutorials that offer tips and tricks to help you successfully sew elastic waistbands.
How to Add an Elastic Waistband
Legging Lovers Guide : Elastic Vs. Yoga Waistbands - differences
Tutorial: Adding Boning to a - Gertie's New Blog for Better Sewing
Tutorial/Video: Sewing elastic into waist tunnel casing in ONE
Would there be any way to loosen this elastic? It is about an inch
Tessuti Multi Elastic Waist Skirt: A Sewing Tutorial - Sew Tessuti
Elastic Waist, Cuffed Crew Trousers Tutorial - Chalk and Notch
5 Ways to Sew an Elastic Waistband — SARAH KIRSTEN
Eureka! Pants that Fit - Fit For Art Patterns
Sewing an Elastic Waistband - Threads
How to make a circle skirt with an elastic casing waistband