Do prepare different versions of takes.
This is especially important if the sides are short, like for a commercial. Even if you are only asked for one take, knowing you have others at the ready will make you that much more confident.
Do bring a hard copy of the sides.
Even if you are completely memorized, it's a good idea to hold a copy of the sides in your hands, just in case you forget your lines. And if you are not off book, you'll want to have your own copy anyway.
Do dress to suggest the role for which you are auditioning.
Playing a doctor? Wear a lab coat. A lawyer? Wear a suit. You get the idea.
Do leave it all at the door.
This is a tough one, because of course you want the part. But the moment you leave the casting office or submit your tape, forget about the audition. You'll cause yourself unnecessary stress fretting over whether or not you gave a good performance. Let it go and move on. You might be pleasantly surprised a few days later if you get a callback or even better, get booked. But if that call doesn't come, it won't matter because you will have already moved on to the next thing.
Don't rely on your phone.
Many actors will rehearse their lines by reading them off their phone rather than printing out the sides. What happens if the phone dies mid-audition? Or if there's no cell service? To reiterate a note from above: bring a hard copy of the sides.
Don't use a prop that won't fit in your pocket.
Props often get in the way and distract from the performance. More often than not a prop is unnecessary. Trust that the casting director will provide any props needed for the scene. If you are submitting a self-tape, unless the item is small enough to fit in your pocket it's probably best to avoid using it.
Don't try to impress.
It sounds counter intuitive, but the moment you walk into the room and try to impress those on the other side of the camera, you run the risk of coming across as disingenuous. Casting directors can tell if you are trying too hard.
Don't play the role a certain way because it's the way you "think" they want it to be played.
Casting directors want to see YOU and what uniqueness you bring to the role. They don't want to see you come in and try to read their minds, acting in a way that feels inauthentic. You might be the perfect person for the part, but they'll never know it if you are focused only on delivering the copy in a way you've decided they want to hear it. Letting go of any preconceived notions of how the role should be performed will keep you open to direction as well.