Basically all you're doing is creating a SC (single crochet) around the strap.
Start as close to the base of the sandal as you can!
-make your slipknot around the strap, leave yourself a 4" or so tail so you can weave it in.
-insert your hook under the strap, yo.
-bring your hook up, yo and pull through.
do this all the way around (even the toe part) and when you get to the other end, leave another small tail slip stitch and thread yarn through a tapestry needle.
-bring the yarn up through the inside of the strap, pull tight and cut yarn. smooth it into the strap so it's invisible.
For the rose I used the same pattern from the winter wreath and attached it with the tapestry needle and hiding the yarn ends the same way.
This was a very quick and easy way to spruce up some cheap sandals. Give it a try!