I've been an artistic director and a stage manger before so let me see what I can do here to try to help. If you are referring to film, I'm not the one to ask as I've only ever been in one film and have never even auditioned for a second one (Film isn't my thing). But I know theatre and many of the same rules apply to both. Hope something here helps.
First off, the number one thing is there are no small roles. If you are auditioning for a role with one line, you have to treat it as if you are auditioning for the lead. Otherwise, the person who took the audition seriously will probably get it because their presence tells casting directors that they care more and that they are willing to better dedicate themselves to the project. Even if you think the part is stupid, just go with the old adage and "fake it till you make it."
Show confidence, but not cockiness. Confidence makes people like you, but cockiness can make someone dislike a perfect stranger.
Be prepared. Prepare a monologue/music piece to perform unless you know the material will be provided at the audition. If music is a part of it, bring your own music (CD, flash drive, or piano music sheets. I also strongly recommend bringing a backup copy in case disaster strikes like it's prone to do). A first audition is of similar material, not the material from the show for which you are auditioning. If one were auditioning for Sweeney Todd, singing a Sondheim piece would be smart, but not singing Sweeney Todd exactly. Same for non-musical theatre. If you are auditioning for the role of Romeo, memorize something from Hamlet or Cymbeline, but don't audition with anything already from Romeo & Juliet. (Those kinds of auditions are after call-backs and the casting director(s) will generally tell you what to prepare for that audition.) Oftentimes, smaller roles won't even have call backs, so don't bank on that "second chance" always being there either.
Personality is important. Nobody warms up to a robot. So smile and be yourself- friendly and easy-going. Everyone gets nervous sometimes so that's natural, but try not to let it overtake your personality or people will remember your nerves more than your talent.
Wear something that says you're serious, but not boring. Wear something memorable, but that won't distract from your performance. (For example, I sometimes wear black dress pants and a nice, striped black and white shirt. Nothing special, but I throw on a thin, red scarf and red shoes because those "pop" and will give the casting director(s) something to connect to a mental image of me.) Some people suggest practicing in your audition outfit so you don't get there and realize you're unable to think about anything but your itchy sweater or uncomfortable shoes.
When you practice for your audition, practice with distractions. I read something recently from an actor (I vaguely want to say it was from Sebastian Stan) who said he did an audition where the director was preoccupied the entire time and never even looked his direction as he auditioned. Yep, that's rude. It wouldn't matter if you gave the worst delivery of your life or if you could have taken home an Academy Award for the performance, that director is a jerk and won't ever know the difference. However, you can't let it change the way you perform. You do the best you possibly can. Be prepared for phones ringing, people talking over you, and a baby crying outside the door. You never know what could happen, but it will be remembered it you get to distracted/flustered to continue.
Always thank the casting director(s) when you're finished. No matter how good/bad you think the audition was, be polite. Never apologize for mistakes. Everyone makes them. And always thank them even if they were rude or didn't respond like you hoped. Manners are important.
And always remember that not getting a role doesn't mean that you weren't good. I have turned down many wonderful actors. It usually just means they weren't what I was looking for. Always persevere.
Break a leg.
