To make sure you have a good audition you must practice your lines a week early like as soon you get a letter about the audition you practice your lines with a friend.
Have a audience when you practice whether it is your friends or family members so they can tell you what you need to work on in case you mess up.
They can also help you with stage fright because I know some people have stage frights, always have confidence and just read your lines out loud.
Have a good tone in your voice when doing your practicing your lines so you know which tone of your voice sounds better like if the lines calls for a dramatic scene have a hint of attitude to make and sound dramatic.
Always double check on your lines and your voice that is exactly what the judges are looking for that and your acting skills.
It is okay to be nervous but try and not to show it or else things could get bad.
Practice Practice and Practice. It will help you I guarantee it.
Hope this helped :)
Have a great day