A travel guide is extremely useful when travelling in Shanghai. Be sure to find an up to date edition, as the city changes from year to year, and a hot restaurant one year may not even exist the next year, or may have moved to a new location. With most people carrying iPhones these days one of the easiest ways to get up to date information are apps. (Remember that international data charges on some iPhones can be prohibitively expensive in China.)  Some of the best on Shanghai:

SmartShanghai - used by all the locals. Heavy on data usage so best if you have a local sim

Zhaocards - equivelant of having a witty, suave concierge in your pocket who knows all the ins and outs, the perfect itinerary and helps you talk to the locals to boot

Most of the other guides are simply ports from the physicals equivalent. Also useful but rapidly out of date!  

Supplemental Reading:

Shanghai: The Rise and Fall of a Decadent City 1842-1949 by Stella Dong is a great account of the glamorous era of Shanghai's past.

New Shanghai: The Rocky Rebirth of China's Legendary City by Pamela Yatsko is one of the best accounts of Shanghai's recent history. 

For a bit of fiction, one contemporary piece is Qiu Xiaolong's Death of a Red Heroine, a mystery about a murder in 1990s Shanghai.