One of the biggest mistakes young actors or new actors tend to do when entering the business of acting and auditioning is that they read the script and do exactly what the writer has written. That is good in some cases, however, the writer has written his or her script with many hints as to who and what the character is and what the character wants. If you do it exactly as written, you are doing what I call a generic read. I am not saying change any words as that is a NO NO! Always consider the writer as the gift-er and gleam all the hints that is in the script, about the character.
Using your own spine, and creating a back life, IE : Who am I, were did I grow up, what was my family like, what were my dreams, what is it I want to do, what is it I want to happen, What do I want the other people in the scene to do or what do I wish to communicate. These are called Objectives, Intentions and are very important to the actor and also they help create choices that will make your audition different then all the other actors coming in for the role.
Also be open to change in your choices. A casting director looks at how you take direction. Also directors want to know that you can not only cold read on the spot, but can make a change of direction if they ask you to.
A big mistake for children is to memorize perfectly the script. It is hard at that point for them to make any changes. I always have my students do the scene and then I have them Improvise the scene and this helps them play the scenes in their own words and then it helps them make choices that are natural to the script as well as to their own truth in the moment.
Remember: Any Choice is better then NO Choice!
In Hollywood you are called in off your picture and so you already have the look. Now make the choice.