Where to put twill tape?

The answer may be obvious, but as a new sewer, I'm clueless!

I'm nearly nearly done with making my first skirt (the Beignet by Colette Patterns). One of the last steps is to apply twill tape to the waist seam, but does that mean... right on top of the seam? Just barely covered by one edge?

The current state of the skirt:
-Facing/lining is attached to the self (5/8" seam allowance)
-Pieces are currently right side-to-right side

I am using 1/2" wide twill tape... Also, do I sew it down the middle or sew down both edges?

I assume there's a facing of some sort on that pattern.  In that case, just baste in the twill tape so that it will lie totally enclosed by the facing when you've turned it. You shouldn't see your stitching line from the outside at all.  You'll want to catch it in the seam though so that it does the work that it's supposed to do (i.e. stabilizing the waist to keep it from stretching out). 

Thank you! That's what I did. Am very pleased with my new skirt.