This paper presents an effective and time saving procedure for designing a three-coil resonant inductive wireless power transfer (WPT) link. The proposed approach aims at optimizing the power transfer efficiency of the link for given constraints imposed by the specific application of interest. The WPT link is described as a two-port network with equivalent lumped elements analytically expressed as function of the geometrical parameters. This allows obtaining a closed-form expression of the efficiency that can be maximized by acting on the geometrical parameters of the link by using a general purpose optimization algorithm. The proposed design procedure allows rapidly finding the desired optimal solution while minimizing the computational efforts. Referring to the case of an application constraining the dimensions of the receiver, analytical data are validated through full-wave simulations and measurements.