Unique features of a liquid marble such as low evaporation rate, low friction, and porous shells make it a useful tool for microfluidic applications. These features are inherently related to the liquid marble shell which affects its effective surface tension (EST). A long-standing problem of liquid marble-based technology is the inconsistency of the EST values. In this work, we determined the EST using natural oscillations of a sessile liquid marble and investigated the effects of liquid marble preparation methods. We proposed a systematic preparation method that improves the consistency of the EST.