Consistency.
On all of my audio systems, since the mid 70's, I've followed this simple setup:
The White or Black terminal gets the silver wire, or the insulation with the white stripe
The Red terminal gets the copper/gold colored wire, or 'the other one'.
There is no pos/neg in the actual wire...just as long as you are consistent.
(and interestingly, a couple of the actual wires I have hooked up to my current 5.1 system are the same actual speaker wires from the 70's...

)