В or на - where do I go to find out?

[lillilah]

I'm a huge fan of the Викисловарь and can usually find answers to my questions there, but this time I can't. So, how do I find out if I should use в or на with a place? There are the ones that I have already memorized, like "на почте" and "на заводе". However with new words, I go to Google to see if I can guess from search results. I would like a better way. Is there some element in the Викисловарь entry that would indicate which one to use? Спасибо!