Cut a macrame lace strip to be just as wide as the bottom of the curtain. Pin your lace in the location you want it along the bottom of the curtain. Use a ruler as you go to make sure the top of the lace is even with the bottom of the curtain.
Using a ruler again, add and pin your next line of macrame lace and repeat with each layer you want to add.
Apply fabric glue along the top edge of each piece of lace to secure (or sew along the top line with a sewing machine).
Add some Fray Check to the ends so the macrame pieces won't unravel.