Providing guidance to customers in a shopping mall is a suitable task for a social service robot. To be useful for customers, the guidance needs to be intuitive and effective. We conducted a four-phase qualitative study to explore what kind of guidance customers need in a shopping mall, which characteristics make human guidance intuitive and effective there, and what aspects of the guidance should be applied to a social robot. We first interviewed staff working at the information booth of a shopping mall and videotaped demonstrated guidance situations. In a human-human guidance study, ten students conducted seven way-finding tasks each to ask guidance from a human guide. We replicated the study setup to study guidance situations with a social service robot with eight students and four tasks. The robot was controlled using Wizard of Oz technique. The characteristics that make human guidance intuitive and effective, such as estimation of the distance to the destination, appropriate use of landmarks and pointing gestures, appear to have the same impact when a humanoid robot gives the guidance. Based on the results, we identified nine design implications for a social guidance robot in a shopping mall.