Hi,
Check this video of Gary Winogrand:
2point8 Garry Winogrand with Bill Moyers, 1982
And this one also:
2point8 Jeff Mermelstein Video from Media Matters
Just do it. Be polite, smile, nod, be your self, know what you do and be prepared to explain.
That's all there's to it.
Cheers,
Michiel Fokkema