Atomically flat and chemically controlled oxide substrate surfaces are essential for high-quality epitaxial growth of complex materials and heterostructures. Previous studies have demonstrated in situ thermal preparation of selected oxide substrates, primarily focusing on conventional low-index orientations such as SrTiO₃ (100) and LaAlO₃ (100). Here, we extend these methodologies to a broader range of oxide substrates and crystallographic orientations, including challenging polar surfaces. We present a systematic study of the in situ thermal preparation of SrTiO₃ (100), SrTiO₃ (111), GdScO₃ (110), LaAlO₃ (111), (LaAlO₃)_(0.3)(Sr₂AlTaO₆)_(0.7) (001), and NdGaO₃ (110) single crystal substrates. The substrates are annealed in a vacuum chamber under a controlled oxygen background environment using a CO₂ laser heating system. The optimized annealing conditions produce atomically flat step-and-terrace structures, long-range surface crystallinity, and effectively clean surfaces across all the investigated substrates. Our results establish a versatile, reproducible, and broadly applicable platform for the in situ preparation of oxide substrates immediately prior to epitaxial growth. These results also provide practical guidelines for interface engineering and surface-sensitive investigations of complex materials.