Thread the needle. Put one bead and coin against the outside of the bra cup. You are going to sew the coins in rows, so you must begin at the bottom of the cup and work your way up.
Thread the needle through the bra cup from behind, then slip the needle through the bead and through the coin after that. The bead acts as a spacer between the coin and the bra fabric to help it bounce and jangle.
Sew the thread in one or two loops around the bead and coin and then stick the needle back through the coin hole and the bead and back into the fabric so that your needle and thread return to the backside of the cup.
Test the coin by flicking it a few times to make sure it hasn't been woven on too tightly. If it moves freely then you are ready to tie off the thread and make a knot.
Repeat this procedure for each coin in every row that you want to attach to your bra, moving from the bottom up on each of the cups.