Using GPS/GNSS observations in earth sciences started in 1980 for geodetic purposes, and its scientific uses have reached its peak for the last 10 years. Moreover, IGS International GNSS Service has been providing the high accuracy orbit and clock information for geodetic and geophysical tasks since 1994. Given fact that one aims to obtain high accuracy and precision as well as consistent and homogenous results from the postprocessing of observations, IGS standards are be taken into consideration. In this paper IGS standards and post-processing strategies are summarized which should be implemented for any tasks seeking mm level accuracy and precision.