First you will need a jersey knit fabric you can also cut up an old T shirt. Cut 2 piece of fabric into 8"x24" of course it doesn't need to be perfect mine isn't.
Then you are going to fold both strips in half and sew.
Sew with a 1/4 inch seam allowance, only sew the bottom.
and put one on top of the other making a cross or X shape.
fold one strip in half.
do the same with the other one...
Finally you just sew the ends together and adjust if needed.
and it should like something like this......
Oh yeah I almost forgot have a good and save Halloween!