An eternal question- are there some “rules” about font matching?

As far as I understand by some typographers there are things you need to take care of when matching two fonts. I understand there needs to be some contrast because there’s no use to use two fonts that are almost alike.

If I use Vista sans bold for headings for example what font would be best for body text (except maybe Vista sans regular) and WHY? I would like explanations so I can match fonts by myself in future.

PS. Please, no answers with “Match two fonts that look good together.” That never ment much unfortunately, thanks. :)