First of all, you need to know how to get in. The best trick is to avoid all the pedestrian entrances around the Expo's perimeter, which can be beset by queues, and instead ask any taxi driver to take you to the Madang Road metro station in central Shanghai (or go there by subway line 9). There you can board a special subway line straight to the heart of Expo.
And then what? Unless there is a handy typhoon to keep the crowds down, avoid the Pudong area of Expo for as long as possible; your appreciation of Shanghai, the Chinese and your own sanity could depend upon it. Pudong has the high profile national pavilions, including China and the US. Leave those until night-time, when they show to their best advantage anyway. Start the day on the west bank or Puxi side of Expo, where the corporate world has spent millions doing what World Expos do best: prototyping the technologies of the future, and showcasing a few cool gizmos.
Let the capitalists entertain you: General Motors may be a mere shadow of its former self, but you would never know it from GM's Expo pavilion. Built jointly with SAIC, the giant Chinese carmaker, GM is displaying an electric mini-car that parks itself, cannot crash, and is small and light enough to park in the closet of a high-rise apartment.