Generic interview advice:
Remember lots of people feel nervous so it's nothing unusual and you don't need to worry about being a bit nervous!
Use some deep breathing techniques before you go in (Google it if needed) - not for long, even 30 seconds can make you feel steadier.
If you feel comfortable, you can mention you're a bit nervous just to clear the air. Sometimes putting something out there can weirdly make you feel better about it.
When you're answering a question, don't rush yourself. Try and speak slowly.
Sometimes it can be good to repeat the question back to them to clarify you've got it correctly. Then it's fine to pause to think for a moment about what you want to say!
If you come to the end of your answer to the question and you feel like you waffled, it's ok to clarify. Say, "does that answer your question?" Or loop back around the original question.
Prepare some questions to ask the interviewer(s). Ask about the company, the team, the responsibilities, or the workplace culture. It makes you seem like you're interested and takes the pressure off you for a while.
Remember that the interview is as much about YOU finding out whether you want to work for THEM. If you're not a good fit, then you're probably better off without the job.
Look through the job description tonight (if you haven't already), and think of examples of things you have done that sit against the different skills or competencies. Just scribble them down in columns or a spider diagram.
Most interviews IME are competency based. The best way to answer these is to follow the STAR technique. Google it! If you can think of 2-3 generic answers that fit your role you can usually bring them out. E.g. a time you have managed a difficult conversation / a time when you were managing a challenging workload / a time you had to work on a project with a colleague / a time when you were "thrown in the deep end" / a time when you had to learn something new quickly.