An encased elastic waistband looks professional and is as easy as sewing one extra hem around the top of your garment. A reader asked me how to do it.
Fold over the top hem as usual and stitch in place leaving an opening to thread your elastic through.
Now before you thread in your elastic, sew one more hem all the way around near the top.
In goes your elastic.
This is the finished look. Below my elastic is slightly smaller than the casing I sewed.
And here it is a tight fit.
A similar style is the paper-bag waist.
My tutorial for it can be found here: http://www.sewingdork.blogspot.ca/2011/09/easy-paper-bag-waist-skirt-for-women.html