RS Ophiuchi (RS Oph) is a symbiotic variable and a recurrent nova (RN). We have monitored it with the Nordic Optical Telescope and obtained 30 high-resolution (R = 46 000) optical spectra over one orbital cycle during quiescence. To our knowledge, this is the best-sampled high-resolution spectroscopic data set of RS Oph over one orbital period. We do not detect any direct signatures of an accretion disc such as double peaked emission lines, but many line profiles are complex consisting of superimposed emission and absorption components. We measure the spin of the red giant and conclude that it is tidally locked to the binary orbit. We observe Na I absorption features, probably arising from the circumbinary medium, that has been shaped by previous RN outbursts. We do not detect any intrinsic polarization in the optical wavelengths.