For clothes, you can go to Qipulu Clothing Market, clothes in there are all at wholesale prices. However, if quality is preferred, it is s uggested that you visit these department stores, which always give nice discount at weekend and holidays.

For the mustsees, don't miss the Bund, Nanjing Road, Yuyuan Garden, and if you have time, don't miss the ancient town around Shanghai, such as Wuzhen (乌镇), Xitang（西塘） and Zhouzhuang（周庄). Then, you could extend the trip to nearby Suzhou and Hangzhou for good natural beauties. Suggested that you read about the introduction about these places in advance, and the suggested Shanghai Tours(https://www.travelchinaguide.com/package/shanghai.htm) will be helpful for your to make a travel plan.