How do you stop a cold before it starts?

What are your best tips for preventing a cold when you feel it coming on?
Despite my best efforts to avoid germs while navigating that wretched Petri dish of a campus, I seem to have caught the first bug that came by.

Curses to my feeble diabetic immune system!
I need to not let this turn into a real cold, because I have a super important interview this Thursday, and it pretty much can’t be cancelled unless I am in the hospital. I’d really appreciate any tips…I’m not thinking very clearly.