I recently googled "how to" for making very small width straps. I never did find then what I wanted though there were plenty that suggested using combinations of hooks, cording and the like. Here's one excellent one for lightweight materials. I also didn't find what I'm suggesting (which works) below and while I like to claim being an inventor, I'm pretty sure this is only an adaptation. What's good about it is that it works for heavier fabrics and for fabrics that have been fortified with stabilizers and/or interfacing. 1. fold cording/string into (ironed) fold
2. stitch a 1/2 leaf shape then sew diagonally toward the width of your strap.
3. sew entire length once (I make the leaf shape at the bottom also in case I ever need to turn back again
4. sew second line using piping foot or the zipper foot (one that will allow you to sew without smashing into or sewing into the cording). Push directly against cording but do not catch it.
5. trim away extra
6. pull cording so that leaf shape turns on itself
7. pull until completely turned
8. trim cording
9. pluck remaining cording with tweezers
10. cut lengths as needed (discard leaf shape)