We attempt to maximize the capacity of magnetic induction communication in strongly and loosely coupled regions. In a strongly coupled region, we investigate frequency splitting, which disturbs the resonance of transmitter and receiver coils. We find a splitting coupling point, which is the value just before frequency splitting occurs, and propose an adaptive frequency-tracking scheme for finding an optimal frequency. The proposed scheme compensates for the degradation of capacity and so guarantees large capacity even at regions where frequency splitting occurs. Next, in a loosely coupled region, we derive an optimal quality factor for maximizing capacity in a two-coil system. As the distance between coils increases, strong resonance is needed to overcome the serious attenuation of signal strength. As a result, the optimal quality factor should be increased. In addition, we find an optimal quality factor for a relay system in order to guarantee reliable communication at long distance. In addition, an optimal-Q scheme that adjusts the optimal quality factor according to a given distance can achieve near-optimal capacity. Finally, through simulations using the Agilent Advanced Design System, we demonstrate the accuracy of our analytic results and the effectiveness of the proposed schemes.