Landau-Lifshitz equations and spin wave damping are derived from first principles by the spin operator diagram technique for the Heisenberg model with magnetic dipole and exchange interactions. It is found that spin excitations, which are determined by poles of effective Green functions, are given by solutions of the linearized pseudodifferential Landau-Lifshitz equations and the equation for the magnetostatic potential. For a normal magnetized ferromagnetic film the spin wave damping has been calculated in the oneloop approximation for a diagram expansion of the Green functions at low temperature. In the framework of the Heisenberg model the magnetic dipole interaction makes a major contribution to the long-wavelength spin wave relaxation in comparison with the exchange interaction. It is found that the damping decreases with increasing film thickness and applied magnetic field and increases directly proportionally to the temperature. For modes of high orders the damping is higher than for the first spin wave mode.