We've posted before about the making of voodoo dolls, but here is some advice from the historically well-regarded Key of Solomon for how to treat the materials and the prayer to say over the charm.
OF WAX AND VIRGIN EARTHWAX and Virgin Earth are also employed in many Magical Operations, whether to make Images, or Candles, or other things; therefore they should never have been put to any other use. The Earth should be dug up with thine own hands, and reduced to a paste, without touching it with any instrument whatever, so that it be not defiled thereby.
The Wax should be taken from bees which have only made it for the first time, and it should never have been employed for any other purpose; and when thou shalt wish it to avail thyself of the one or the other, thou shalt before commencing the work repeat the following conjuration:--CONJURATION.EXTABOR, HETABOR, SITTACIBOR, ADONAI, ONZO, ZOMEN, MENOR, ASMODAL, ASCOBAT, COMATOS, ERIONAS, PROFAS, ALKOMAS, CONAMAS, PAPUENDOS, OSIANDOS, ESPIACENT, DAMNATH, EHERES, GOLADES, TELANTES, COPHI, ZADES, ye Angels of God be present, for I invoke ye in my work, so that through you it may find virtue and accomplishment. Amen.After this repeat Psalms cxxxi. xv.; cii.; viii. lxxxiv.; lxviii.; lxxii.; cxxxiii.; cxiii.; cxxvi.; xlvi. xlvii.; xxii.; li.; cxxx.; cxxxix. xlix. cx.; liii.; and say:--I exorcise thee, O Creature of Wax (or of Earth), that through the Holy Name of God and His Holy Angels thou receive blessing, so that thou mayest be sanctified and blessed, and obtain the virtue which we desire, through the Most Holy Name of ADONAI. Amen.Sprinkle the wax and put it aside for use; but take note that the Earth which should be dug up with thy hands should be prepared every time thou hast need thereof.