I will show you how to use a standard shoelace as a Geta strap (thong) to add some western flare to your eastern footwear.

You will need:
a pair of geta with the toe loop already installed
and a shoelace

The shoelace can be decorative or plain.

If you need help making a pair of wooden sandals, there is an instructable for that:
www.instructables.com/id/Make-Your-Own-Geta-Sandles/

Step 1: Loop the Toe Loop

Loop the toe loop of your geta so it can hold the strap.

Fold the top of the loop down to make two loops on the end.
Fold the two loops together.

Step 2: Add the Shoelace

Place the shoelace through the toe loop and shift it so the ends of the shoelace are even.

Feed the shoelace through the holes in the rear of the geta and pull them tight.

Step 3: Cross the Shoelace

Feed the shoelaces up through the opposite holes and pull tight.

Step 4: Adjust the Strap

Pull the shoelaces back a little so they are loose.
Insert your foot and pull on the shoelaces to adjust them to the size of your foot.

Step 5: Finalize the Strap

Remove your foot being careful not to change the adjustment of the strap
Loosen the toe loop
Feed the shoelaces through the toe loop
Make sure the shoelaces are adjusted the same as the old adjustment
Tighten the toe loop
Tie a knot in the shoelaces over the toe loop