This paper proposes a design strategy for a wide-area measurements based power system stabilizer to improve the mode of concern, which is the dominant inter-area mode, in each system operating point. The strategy includes two steps: feedback signal selection and controller parameter tuning. The principle of the feedback signal selection is to maximize the residue of mode of concern for the feedback signal while minimizing that of other modes. Then the tuning process can focus on only the mode of concern. The proposed design strategy has been tested on an operating point of the IEEJ East 10-machine system. The result shows that the designed controller can improve the mode of concern significantly, while it can not affect much the others.