Several practical criteria to improve the performance of a mixed FDTD-MoL method of electromagnetic analysis are proposed. Concepts as the properly dimension selection of the waveguide “containing” the microstrip geometry, the true propagation speed on the microstrip, the suitability of the excitation pulse spread and the relation between the reflected and incident waveforms, the preservation of both, the time and space derivatives for the FDTD segmentation-discretization part, and the analytical incorporation of the boundary conditions are all discussed.