Make a slip knot with 2 strands of yarn held together.
Holding the yarn across the top of the flip-flop strap, reaching under the strap, catch the yarn leading from the balls with the hook. You now have 2 (double strand) loops on the hook. Wrap the yarn around the hook and pull it through both loops. You have now made a single crochet. Repeat until the strap is completely covered.
When the strap is completely covered, cut the yarn to 5" and pull the ends through the last remaining loop. Thread the yarn needle with the yarn end and pull back through a few stitches to hide (you can also use a crochet hook to do this). Trim the end.
Although you can start at the end of one strap and crochet straight across to the other side, you will get better coverage by starting at the toe end of each strap and working back, then returning to the toe end to do the other side.
For a very furry look, it is easier to push the stitches tightly to the toe. Optional Finish your flip-flops by gluing a large button, rhinestone, or beads to the toe.