We present an outline on the use of ellipsometry for nematic liquid crystals characterization. Possibility of anisotropic refractive indices measurement with accuracy up to 10-4 is demonstrated in the visible and near infrared wavelength ranges for different temperatures. Liquid crystal director distributions were measured both in cells with and without an applied voltage, subsequently the values of pretilt and polar anchoring strength were obtained by fitting the experimental data. Especial attention is paid to modifications of the commercial ellipsometer and to the choice of the proper data acquisition mode which improve the reliability and accuracy of measurements.