I assume you are enquiring about fashion. Personally I love luxury, so I always look for outlets and second-hand shops for good bargains too.
If I want to see where the trend is, to me nothing beats Grieder, in Zurich. The whole area of Banhofstrasse is anyway a pleasure for the fashion eyes, but very expensive.
Here are my preferences in Zurich.
Best Luxury Store in Zurich
Best Second Hand for Luxury
Best Outlet in Zurich
Best Outlet in Switzerland
Best Shops in Switzerland
Here is a general shopping guide by Time Out you might want to consult.