And the second principle is, put the attenuator as "late" in the signal flow as you can while still protecting the input that you need to protect. That way, the signal in the wires leading up to that point will be unattenuated, thus increasing its immunity to interference (hum, buzz, RFI, cell phone/Blackberry noise, etc.).
So, for example, if you're padding down the inputs to a recorder, put the pads at the recorder's end of the cables--not at the outputs of the device that's driving the recorder's inputs.
--best regards