If there is a turntable, dress the power wiring opposite the arm and keep the arm as far away from transformers as possible.

When practical, keep signal wiring away from power transformers and cross power and signal cables at right angles. Keep signal wiring away from modular power supplies.

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Years ago I was working on a tube power amplifier that had hum in the speakers. The obvious candidates for replacement were the power supply filter capacitors, but this did not help much. I noticed that the hum did not track the Volume control. This was not shocking, but then I noticed that there was hum when all of the tubes were removed. Stepping back, I observed that the power transformer and output transformers were very close and their laminations were in parallel. Not a very glorious solution, but I moved the output transformer off chassis and the hum was gone. (Rotating one transformer 90° was not good enough)