This poster paper presents the analysis, the design, and a first prototype of the Optimized Slits Positioner Software, a part of the EMIR Observing Program Manager System (EOPMS). EMIR is a multi-slit near-IR spectrograph presently under development for the Gran Telescopio de Canarias (GTC). This tool represents a crucial step for the success and efficiency of multi-object spectroscopy. Complex algorithms have been implemented to help the observer in designing and validating the mask sets, both automatically and interactively, through a user-friendly interface.