Lots of prep in advance is a bit chunk of what will swing it for you.
Going in to that interview really familiar with what they're looking for, and adding your own unique contributions on top of the 'must-haves', with the experience they can benefit from.
Make it an interesting interview for the recruiter. Show them why you will add value to their department. They want you to be the solution to their recruitment problem.
no need to grin or smile too much, save it for the opening and closing of the interview, a gentle smile in response to relevant stages in the interview will make you come across as controlled and professional.
Carefully reading through the role spec, focusing on the must-have criteria and think about how you can meet those needs.
Less is more - try to speak slowly, leave space between your sentences (breathe! Breathe! Breathe! ) so it isn't the verbal equivalent of a "wall of text" and you aren't left gasping for breathe. Quality not quantity, it isn't a competition to cram the most words into a minute, it's the content, what you say that matters.
Stick to the point, don't ramble to fill the silence. Saying one relevant thing will help them much more than a barrage of words, with them having the problem of pulling out the value-add. Make it easy for them to see why you're the right candidate.