Real life pitches are my favorite thing, probably because I worked as a pitch person for products professionally (say THAT five times fast - yikes). Some of my advice might contradict other people's advice. That's fine - we all have our own ways. But I'll be real with you -- I see people up above recommending five to six minutes pat on a pitch, and that's a ridiculously huge chunk of time - being talked at that long about anything by anyone gets boring/tedious/hard to follow. Even when it's well thought out, organized, and interesting. Literally time that out -- give it a try. It's exhausting.
I'd suggest having a significantly quicker pitch (60 - 120 seconds), talking points, and bringing a physical copy of your query letter, if they want to see it after your short / elevator pitch. They read faster than you talk, and less awkwardly, and I've yet to have an agent decline to do so.
Start with introducing yourself - don't jar straight into the pitch like the agent is a pitch listening machine. They're a person - hi, my name is, I'm excited to meet you, love the shoes. I wrote a category + genre novel. Would you like to hear my pitch?
A note card with bullet points will help you stay focused if needed - pitch, comps, questions, in descending importance.
Know your pitch, and practice it in a mirror. Practice your pronunciations, your stance, what you do with your hands.
Find other writers at the venue to practice with! A quiet room with a mirror is a very different environment than with other people! Honestly, this was the most valuable part of pitch conferences for me - networking with my peers, practicing pitches, refining things with newfound friends. You're all nervous, you're all excited, this is one of the few parts of writing that you aren't doing entirely alone.
When it comes time do to your pitch, remember the agents WANT you to do well - it's way less awkward for them if you do well and have a premise they can get excited about. They don't want to crush your hopes and dreams right in front of you, y'know? A lot of agents are ALSO introverts and just as nervous as you are. They're book people too, a lot are introverts.
Agents are people. Treat them like people. If you love their earrings, you can say it instead of staring awkwardly at the earrings (yep, been there, done that). If you're nervous, they won't suddenly turn into a dragon and swallow you up for admitting it.
If you're uncomfortable in your outfit, you won't be able to focus on the pitch. Clean, tidy, and comfortable is better than clean, tidy, and stressing out about your leggings or hair.
If you really love your book, you have a solid pitch, and you know your market, you're already doing better than three quarters the people you'll meet.
Oh, and do try not to be late!