Unfortunately, not all of us are professional models/ actors.  So, as a photographer, I've seen a lot of tricks to get people to look candid in portrait-type settings.  From telling a bride to make a serious face until she cracks up to making an awkward comment to get a response from a couple, I'll admit... I'm guilty of at least trying most of them out at one point.  However, when people are comfortable and genuinely having a good time, it shows.  That's why when shooting an individual, I usually suggest that they bring along a close friend or two.  I say "close friend" because sometimes your best friend may not be the best person to bring with you to your shoot.  The key question to ask about your best friend before asking them to come along with you... "Will this friend pick at me to the point of annoyance?"  Plain and simple...your photo shoot is not the time to be self-conscious, or stressed out, but then again the friend (or friends) you choose shouldn't shy away from telling you that you're doing that dance recital/ cheerleader competition face again (you know the one... we all do it) either.