The main thing is to reduce or improve the connections, especially on the power supply circuit.
That, and use an alternator that will supply the power needs of your car at idle.
Power supply circuit is from the alternator to the main junction (a welded splice) when the alternator is doing its job.
Power supply is from the battery to the main splice when the engine is off or being started.
Simplified diagram; On a car with ignition switch in the column, there's another connector.
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