Few suggestions:
-picture size > 600x800
-Light preferably from front
-Keep your shirt open enough to have a clear background for the jewel.
-I believe that a smile makes the best portraits, but that's your choice.
-send as well your name, the place where you come from and, if you like, a small note.
-by sending the picture you agree having it published on this web site (no information will be given to third parties)