Some common mistakes to avoid during the mixing and mastering process include over-processing the audio, improper use of EQ and compression, neglecting proper gain staging, excessive stereo widening, and not leaving enough headroom for mastering. It’s important to maintain a balanced approach, use processing techniques judiciously, and ensure that each element in the mix has its own space. It’s also crucial to reference your mix on different playback systems to ensure it translates well across various environments.