How to succeed at auditions
All types of auditions are different; a casting for theatre will be nothing like a film casting or a commercial casting. Auditions are quite strange situations to be in but there are some general guidelines which are advisable to follow.
Whatever kind of audition it is, be prepared. This starts before you even get to the audition! If you have been given a script before the day - read it! Read (and learn) the lines you've been given and read as much as possible around it to give you a good idea of the story. If you've been told to do a monologue - practise it and learn it. You may have a monologue that you've been using for a while but it doesn't hurt to go over it again. If you haven't been given anything to prepare in advance, then be prepared to learn and adapt as much as possible in case you're given a script when you walk in the door.
This is obvious. First impressions count and if you can't turn up to an audition on time why would they think you'd make the expensive shoot on time. Don't turn up looking like you've sprinted the last mile because you were running late. Make allowances for travel disruptions or getting lost then, if you do have to run the last bit, you'll have time to freshen up in the bathroom before you go in. But more importantly, be early so that you can learn any script you're given beforehand.
Now you're at the audition, the main thing with is to be yourself. Unless you're really miserable then don't be yourself - you could write a whole different article on this - but the general consensus is to come across as happy, friendly and willing. You want to come across as someone who is easy to work with, in case you do get the job. You need to be willing to take direction or even wait around 10 minutes in case they're running late. Which they probably will be - but that's more time for you to learn your lines.
When you're reading over the script you immediately have an idea of what you think the character should be. That's excellent. Go with it. Enter the audition with your take on the character and be committed throughout the performance - however silly you think you look. The casting director may have had a completely different idea of the character, but it's subjective, there's no right or wrong. If you present your idea, they know you're serious. They might ask you to adapt it completely or they might have seen things that they'd never thought of before and work those in somehow. Either way they can see you're prepared and willing.
Don't over complicate things. If in the script there's a note that the characters are in a car, then you might be provided a chair. Sit in the chair and act. Don't worry about miming a three point turn, whether it's in the script or not, it detracts from your acting! Right now, all they want to see is your acting. (Unless of course the audition is for a mime!)
Hundreds of people probably applied for this job and you're one of the lucky ones that gets to be seen by the casting director/producer/director/assistant. You may only be in there for 5 minutes, but that's a valuable 5 minutes to show them what you've got. Before and after the acting part, make brief friendly conversation, but don't ramble on. Politely thank them before you leave and be polite to everyone. The person who took your name could be the director's sister's niece's friend and you can be assured that they'll let everyone know if you're rude.
After you've presented yourself in a friendly way and you've nailed the audition with confidence, the situation is out of your hands. You've done your best and there's nothing more you can do. You might see the project being broadcast in a few months and think you did a better job than whoever it was that they cast - and you probably did. Although your acting was just what they wanted, you might have had a slightly different look to what they wanted. It's not your fault, there's nothing you can do and if you beat yourself up about it you'll ruin your next audition.