Step 1: Make your costume
FIRST: get a long white dress for your model. i got one from a thrift store for $3 which I highly recommend if you plan on cutting it up or throwing dirt on it like i did.
NEXT: cut it up and make it look worn & torn. i threw dirt, flour, and red food dye mixed with vinegar and then olive oil on the dress my model wore to make it look authentic and as if she just rose from the dead after a bloody, violent death.