Basic "inner game" tip: don't be too attached to the outcome. You'd like it, but you can take it or leave it.
generally agree with this. it's a balance: be confident and relaxed, but not obnoxiously entitled, overly casual or standoffish. if you really want the job, show genuine interest but not desperation, project the aura that you're happy with your current situation but meeting with them because this particular opportunity sounds interesting. don't make it seem like you are interviewing all over the place with lots of other employers.
it's a little bit like a first date: be yourself, communicate what you're all about and have to offer, be respectful but leave them with the notion that they'd be better for having you on board.
I'm self-employed, so my story relates to a meeting for a potential project (which is similar to a job interview). the guy who I met with had apparently cut himself shaving that morning, and had a small wad of tissue stuck to his face to stem the bleeding. it wasn't an oversight, he obviously knew it was there, I guess he had no choice.
cutting yourself shaving happens sometimes, not a big deal. the weird thing was he never mentioned it, so there was this odd unspoken tension for the entire meeting (I imagine if I were in his shoes, I'd have made a joke about it to diffuse the situation). and of course, I found myself continually focusing on the small bloody wad of tissue attached to his face while he explained his company's work for a particular client and how the firm sets itself apart from competitors. it was almost farcical, felt like I was on some hidden-camera TV show where they film a person in an absurd situation to see how they react.
I ended up not getting the assignment, and I was kind of thankful. probably symbolic in a way, anyone who couldn't bring themselves to make a joke about something like this would probably be kind of a dick to work for.
good luck!