Careful about whispering! It is actually more strain on vocal chords than normal speaking. (If you speak normally, but quietly, it is better.)
Drink lots of water (lukewarm is best), get lots of vitamin C, and -- funnily enough, this is something my singing teacher told me when I was younger -- pineapple juice is better than orange juice. Orange juice is not good because it is acidic, but pineapple juice is good because it is alkaline... And a lot of what makes your throat sore is the extra acidity at the back of your mouth when you get a cold. Also, freshly squeezed or juice from a carton is better because it hasn't been exposed to sunlight and therefore retains more vitamin C.
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"We're an anarcho-syndicalist commune."