When we don't prepare for an audition that's when self doubt starts to creep in, nerves show up, and we don't present our best selves.
The challenge for most actors is "What is the preparation work?" The important thing here is to develop a system that works for you, and stick to it.
1. Do not perform your script when you first get it.
Approach your script as an investigator. Read through it (in your head) as an audience member and start to highlight some important points of the story. Then, read through the script a second time, and write down any important things you might have missed. Then, you'll want to read it a THIRD time from a director's point of view. Really pick up on all the details as well as the bigger picture. Try to stay disciplined and go through the steps one by one.
2. Do not daydream as if you have already gotten the role.
This puts your focus inwards. When you go into an audition, you want your focus to be on the story, the character, and the stakes that are present for your character. If you're focusing on getting the job, you won't be present with your scene partner, and you will bring in desperate energy. Go into your audition with excitement about the story you're telling.
3. Art of Discovery
Approach your scene with childlike wonder. You're taking in new information, so allow it to inspire you and spark ideas. The first three read throughs are essential. Make notes on the discoveries you make from the relationships, the themes, the inner and outer conflict, the character's wants vs. needs, etc. Once you have all this work done, then you can move out of your own way.
Hopefully these steps help you develop a system that you can use each and every time you work on a new scene.
Don't forget to have FUN with the work!