The following have served me well:
1. Initiate the conversation with small talk. It allows you to take the reigns, and guide the conversation. Otherwise they will do the honors, and inevitably it will go to places you don't want it to go.
2. Go on to the front foot from the get go. If you sit back, waiting for them to ask the questions and hoping you can get the answers right, they will eat you alive. Instead, be proactive, take the initiative, show (feign?) curiosity by asking intelligent questions about the role, the company, the office, the city (which requires you to have researched all of these details), questions which just about border on the skeptical without crossing the line into outright dismissiveness.
3. Always leave them wanting more. When asked to explain a project you did, don't just jump into a detailed explanation which will be hard to digest and prompt them to move on. Say a bit, stop at just the right point, and then wait for them to ask you to explain some part of it that they are interested in. The important thing here is to make sure they ask about the details you want them to ask.
4. Humor and self-effacement are a potent combination. It makes them empathize with you. Like with everything, moderation is key. You don't want to come across as either a clown or someone wallowing in self-pity. But small, judicious doses of humor and self-effacement work wonders. I've been lucky in that both come somewhat easily to me.
5. Last but not least, I always tell myself that the worst that could possibly happen is that I won't get the joke b. Unless I'm starving, homeless and completely broke, it isn't the end of the world. There will always be a next time, and then another, and another, and so on and so forth. If you begin your career at 22, and retire at 65, you'll have a career of 43 years, and there will be many many job interviews. You will fail most of them.
