There it is no recipe for what it is selling!
A painter paints 1000 painting in his life , only 10 of them are masterpieces that sell at private fund rise ...
One example it is one of my country sculptor Constantin Brancusi
http://en.wikipedia.org/wiki/Constantin_Brâncuși his works did not give him million of dollar when he was alive , neither today his family does not get big bucks , but his sculptures are sold now at : Constantin Brancusi, Oiseau dans l'espace (Bird in Space) Price - $27.4 million
I see jewellery making as sculpting.
All depends the way you market your product and target clients in the end , dose not mater what you sell , toothpicks or jewlery , car or houses.
Due the diversity nobody in here can`t tell you "what sells"
I can make a sculpture that for me "sucks" then next day see someone buying it ... people taste it is dynamic , and you must chose what client you have in mind and make a product for that client.
Some recommend to search some marketing expert to give you some insight ... some just only want to take your money and say crap ... some just say to do it your way.
I`m not a guru , but I try to do it myself , if I fail ... I keep doing it until I`ll win.
Some people want to keep "secret" how they run their business that it is way they are so "shy" of saying things up ... some hire people to do the marketing stuff .. some got lawyers.
If I think only about money then I don`t create original art , I do crap , and that means that I don`t care "what sells" , I only care that my stuff will be a masterpiece for me ,and become a masterpiece for the world.
.... no going to learn some marketing sop ... and stuff