The method averaging over angles of arbitrary functions of the angles of mutual orientation with the use of angular form-factor is developed for the dipole-dipole and dipole-quadrupole interactions. The functions are averaged by use of a single integration over the form-factor with certain weights, for which explicit analytical equations are derived and the method of numerical calculation is formulated. For the dipole-dipole interactions, the weighting factor is expressed in terms of elementary functions; for the dipole-quadrupole interactions, it is written in terms of the first-kind elliptic integrals, and two approximations are proposed for it.