I'd Google the movie title and "Tracking." In addition, look for articles related to Fandango and movie ticket sales. They are the largest online ticket firm so they provide a great assessment of opening weekend based on the public's actual spending. The Hollywood Reporter and Deadline are also good places for pre-release info. In addition, boxofficeguru and boxofficeprophets provide weekend predictions Thursdays and Fridays based on the existing industry tracking.