I interview people all the time, it's a main part of my job.
Firstly, don't worry about being nervous. It's totally natural and I expect people to be a bit nervous, it's a strange situation. A few nerves can be good for you, they show that you care about the role you're being interviewed for.
Focus on being friendly, smile and make eye contact. Don't worry about taking time to think before you answer a question and say if you don't know. I'd much rather someone say "I'm not sure, but I'd find out by doing XYZ" than trying to bullshit an answer.
Think about things you'd like to let them know. Think of examples from your current and previous work. Take a good look at the job description and try to see how you can evidence that you meet the criteria along with relevant examples.
Always ask questions yourself. One of my biggest red flags is when candidates don't have a question to ask me at the end of the interview. You could ask what they like best about working there, or what their main objective is for 2024, or research the organisation and ask a question about something you've read. Show them you've done some research into the organisation.
I would write down the main points you'd like to get across and relevant answers to questions you think that would come up and read them over and over. It'll help you feel prepared.
Just be yourself, smile, ask questions, be friendly and interested in what they have to say and you'll be great.