Flexible electronics have emerged as a revolutionary paradigm to unlock novel possibilities across diverse fields such as wearables, healthcare, and wireless communications. Among the numerous materials, liquid metal (LM) thin films, characterized by high electrical conductivity, high thermal conductivity, high ductility, and biocompatibility, have become crucial materials for the fabrication of flexible electronics. Nevertheless, the current state-of-the-art technologies still face several challenges including complex preparation processes, poor compatibility with substrates, and insufficient mechanical stability. In this comprehensive review, the innovative preparation technologies for LM thin films including patterned printing methods, various coatings techniques, and interface-driven assembly approaches have been systematically summarized. The underlying design principle which involves modulating the ratio of composition materials and process conditions, are elucidated in detail. Moreover, their innovative applications in flexible electronics are concluded. Finally, we provide a forward-looking perspective on the future research and development trends in this burgeoning field. It aims to guide and inspire further scientific investigations and technological advancements.