I refashioned a shirt that I have.
I used a t-shirt that my husband thought was not soft enough.
I cut 3-inch strips from the bottom of the shirt and pieced them together.
You then change the setting on your sewing machine - the stitch length is the longest that you can get and the tention is the highest you can set it.
Then sew close to one side of the strips and it will ruffle for you. (I learned this on someone's blog, but not sure which one.)
Just pin it on your shirt and sew it on and you can have something like this.
From plain to special.