First of all get the basic information about the audition like where it is and what it is for. Every project demands a different kind of style of performance so you should be well prepared for the presentation.
Try to read the play before you go for the audition. If it is a new play and you do not have the script then try to put yourself in different situations and play different characters. Similarly, if it is a musical play then try to get familiar with the songs. This will help you to impress the judges not only with your performance but also with your knowledge.
Write a sample script for you and rehearse before the audition. It will help you to overcome the hesitation and which almost everyone feels before displaying his talent to the public. Choose a monologue that is appropriate for your age and gender there is no harm in doing experiments as it will show your versatility.
Try to prepare more than one monologue as you may find yourself in a situation where the director wants to see more from you. Sometimes, it happens that you walked in for some specific performance but the director saw something else in you and offered you that job. Be ready for such situations and show your adaptability.
Keep your sample performance short and snappy as the judges will not have much time to evaluate you. A 90-second performance should be enough to show your strengths. Save something for next performances. Let them desire for more.
Be that person when you enter in the audition room. Your attire does matter a lot as it helps the judges to visualise you in some specific character. However, do not wear something you are not comfortable with as it will affect your confidence.
Try to control your nerves as auditions are always stressful. Hold your breath and drink some water. You may seek help from a professional acting coach.