This paper proposes a self-organizing technique for enhancing the coverage of wireless micro-sensor networks after an initial random placement of sensors. A randomized back-off delay time is introduced to resolve the problem of simultaneous movement of sensors in the neighborhood which will lead to unnecessary excessive movement and hence consume more sensors' energy. A sensor node will relocate itself when the time calculated through randomized back-off delay computation is reached. The new location of the sensor is determined by a virtual force-directed algorithm where virtual attractive or repulsive forces exerted by other sensors or obstacles are used to guide the sensor to the desired location. The proposed self-organizing algorithm for sensor placement is proved to be effective through simulation.