National Language - Urdu, Pakistan
I guess this is a universal travel tip, but I proved its worth while travelling in Pakistan.
It really helped break down cultural barriers by having a few Urdu phrases up your sleeve. I won a Hindi-Urdu phrasebook in a competition in Australia and it proved really useful to get me started.
The pronunciation is so hard to get from a book but once I had bumbled my way through a few phrases most people were only to happy to explain in English how to pronounce the Urdu!
Also knowing the universal greeting 'assalam aleikum' goes a long way.........and 'nahii' to tell all those insistent taxi drivers that you don't want a lift!