One of the most used way to tune the parameters of power oscillations damping controllers (like, e.g., the Power System Stabilizers (PSS) of generators) is to provide a phase compensation to 180 degrees of the phase of the residues of the inter-area modes to be damped and, next, to increase the gains of the controllers in order to obtain the desired damping for the aforementioned modes. It is shown here that this way of doing is suboptimal. First, from the physical point of view, there is no a priori reason to compensate the phase to 180 degrees. Next, concerning the damping of the oscillations, when the phase compensation is computed in a coordinated way with the gain of the controller, better results are systematically obtained. This means that, in comparison with the standard way of phase compensation (to 180 degrees), this new tuning strategy provide the same damping level obtained with lower gains for the controllers (i.e., with more robust controllers) or, alternatively, higher damping levels with the same level of gains (i.e., better performances). The optimal parameters of the controllers are solutions of constrained optimization problems for the general case of several controllers tuned to damp several modes. Examples on both academic and real large-scale (the European power system model) cases are given. This result is general and can be applied to any control framework (for classic generators or more advanced (optimal) control, for local, inter-area or other oscillatory modes).