In this work, the focus is on optimizing the process parameters of fused deposition modeling manufactured parts, to improve the tensile mechanical properties of manufactured samples and to investigate the impact of the process on the rheological and thermal properties. Particular attention is devoted to the printing order of three-dimensional (3D) samples (printed in a batch or individually). A comparison is made with samples prepared by injection molding. The optimization results show that the raster angle and build orientation (horizontal or vertical) affect the mechanical properties of printed parts. The most significant parameter for the mechanical properties is the printing order; a significant improvement is observed for samples printed individually. The results also show that polylactic acid samples prepared by injection molding undergo thermomechanical degradation, while 3D-printed samples are not affected by the high temperature of the process.