PhotoComix

Start here:
-Costume Jewlery or 14K gold plated/brass/sterling silver pieces.
-Draw it up so that it look like an actual jewerly piece.
-Colorize/metalize/glitterize it and make it look realistic.
-Make sure you consider that it will not be too heavy a piece to wear.
-Make sure you do matching sets: Necklace, Bracelet, Earrings.
-Go in person to some jewlery stores and show your mockups and ask them for advice. If they really like it they may want to order some pieces... with some orders you can invest some money to get molds made and make multiple pieces for sale.