I needed a cheap, adjustable sling for a new yoga mat and this is what I came up with. I used a pair of round shoelaces, but you could just as easily use paracord or some other rope.
Step 1: Materials
All you need is a pair of shoelaces!
The pair I used happened to by 72" long, but I had lots of extra string left over. Fifty inch laces should be plenty long. Alternatively, measure and cut two pieces of rope - one 30" and one 50" (one of the laces will have to be trimmed anyway). Stay away from polypropylene ropes or anything else that is too slick as this sling relies on friction for readjustments.