Naples is a perfect location for all shopalcolic, specially for girls…;)  Naples is a city full of  inexpensive shops where you can find  shoes, clothes, accessories and craftworks.  
The main street for shopping in Naples is Via Roma ( also called Via Toledo) where there are boutiques, departments store,  franchising and local shops.   You shopping tour can start to Piazza Plebiscito, were there is the famous Cafè Gambrinus.  A perfect place to drink a real Neapolitan coffee witch give you the energy for you shopping full immersion.  From Piazza Plebiscito start from Via Roma and enjoy!  The biggest department store in Via Roma is “ La Rinascente” but, for my personal shopping experience , to buy  cheap clothes I suggest Alcott, Phard and  Berska. 
If  you prefer some of high level from Piazza Plebiscito turn on the left and go up by Via Chiaia where it’s some brand boutiques .  But to find the most important boutiques  you have to go to Via Calabritto ( in the end of Via Chiaia). Gucci, Prada, Armani, Salvatore Ferragamo and Louis Vuitton in fewes  metres!
If you are interested in antiques and craftwork, you should go to historical center: in Spaccanapoli you’ll find antiques dealers and in San Gregorio Armeno you’ll can buy a typical Native Scene for the next Christmas.