Prelude Music
The half hour leading up to the wedding ceremony is when the prelude music occurs.  This is the music that your guest will hear as they are being seated and while they are waiting for the ceremony to begin.  Since this is the first thing that your guests will hear it sets the tone for the wedding ceremony.  Anything goes here!  You might consider songs that your guests would particularly enjoy since they will be the ones hearing the music, and save your favorite(s) for the actual ceremony.

Seating of the Parents
This selection is played during the seating of the parents and grandparents.  Usually one selection is best (about three minutes.)  If there are only two sets of parents being seated you might want to consider using one selection for the seating of the parents and the wedding party.  Since this is the music your parents will be seated to you could consider letting them choose the selection.  Maybe include a selection from your mom's wedding here as a mini-tribute!

Wedding Party Entrance
This selection is played during the entrance of the wedding party.  Usually this is a separate selection from the seating of the parents.  The Last parent seated is the bride's mother.  Next comes the entrance of the groom, then the weddings party followed by the ring bearer and flower girl.  The flower girl is the last person down the aisle before the entrance of the bride.  The groom, wedding party, and flower girls enter to one musical selection.