Surface anisotropy energy density is a key quantity in the description of the dynamics of surface spins in ferromagnetic thin films and is known to result in a ferromagnetic resonance fine structure of a thin film: A multipeak spectrum is observed in an effect known as spin-wave resonance (SWR). The so-called surface pinning parameter, directly correlated with the surface anisotropy energy, plays a fundamental role in determining the character of an SWR spectrum in the theory of SWR based on the surface inhomogeneity model. Here we extend the theory of SWR by introducing a new formula representing the surface pinning parameter as a series of contributions from different anisotropies existing in (Ga,Mn)As thin films. We show how to determine the coefficients in this series by comparing the SWR theory with data obtained in a resonance experiment. The proposed procedure allows one to determine the proportion with which each type of the anisotropy contributes to the total surface anisotropy of (Ga,Mn)As, and, consequently, to assess to what extent the proportions on the surface differ from those in the bulk. The presented considerations can be used for the study of any other thin-film system, since we provide also a general rule that allows one to express the surface pinning parameter of a thin film, as well as its surface anisotropy energy, by the free energy of the considered thin-film system. This enables the interpretation of experimental SWR spectra in terms of the free-energy density of the thin film.