Available at most automotive parts supply houses. Correct or reverse AC polarity on all components, as determined by either multi-meter measurements or through listening. Subtle but telltale improvements in detail and musical cues, perceived as an increase in soundstage and localization information. Depending on the component, you may also notice less grain and grit as a result of a lowered noise floor. Routing of all signal and electrical connections to reduce potential interactions.
Common sense results in avoiding any potential interference from either high or low- level signals.
At least keep interconnects and speaker cables away from each other and from ac cables. If they need to cross each other, then do so at 90 degrees. If they are to run parallel to each other than space at least 6-inches apart. Suspension of signal wire with wood supports, or any thing for the matter. My father made these from Australian redwood, and they are very similar in appearance to those being used by the man with the golden hair.