Factors influence potential customers

A large supermarket chain would like to know what factors influence potential customers to come to their supermarkets. They have asked you to investigate this and build a regression model to estimate the number of customers that use any one of their present supermarkets. This model will then be used to provide information to determine whether to locate new supermarkets in specific towns. What could these influential factors be? Which of these factors could be used in a regression model? How would you go about developing the model? If you were successful in developing a model, what notes of caution would you give the supermarket in using this model?