When you have a voice over audition, you need to remember one key thing, which is that voice over is not reading, voice over is acting. You should put the same sort of thought into a VO script as you would into an on-camera script. Who is your audience? Who are you in relation to them? What is your message? What is your approach? What is the tone? What is the pace? What are the key words in this script that I should hit? How old is this character, how well-educated, how formal or casual? If you are just reading it, you are missing the point.
Second, READ THE DIRECTIONS YOUR AGENT SENDS YOU. Each casting office has their own way they like things to be labeled and slated. If you aren't reading the slating and labeling instructions because your agent usually has you do things the same way every time, you are going to piss off your agent. What they won't tell you is that with all the VO auditions they send out, listen to, and post, if you don't have yours right, they are probably not going to bother to tell you, they are just not going to submit it. And then they may not send you many VOs because you don't read instructions.
If you don't know for sure how to pronounce something, look it up. Don't just guess. Or ask your agent. It's an enormous waste of my time to listen to an audition with words mispronounced because I can't send that to the client.
Don't confirm VO auditions unless specifically asked to do so. I send out on average a dozen projects a week for self-tapes (depending on the season). And I usually send them to 20 or so clients per audition. When my work email goes off, it makes a ding sound. I stop whatever I'm doing to check the email because it could be an audition or a confirmation or a booking. But if it's you just saying "Got it." ???? I would find that out in 2 days when you turn in or don't turn in your audition. Email with purpose. If you have a question, absolutely, but read the email I sent twice before asking me a question because 9 times out of 10 I answer the question in the original email. Remember, there are hundreds of you and only one of me. I know you feel like I have one agent. But I don't have only one client, so please value my time.
Send your VO auditions on time. If you don't, I can't send them in. I have a deadline. When the deadline I give you comes, I have an alarm that goes off. I listen to all the auditions I have, and upload them all as a zip folder. I can't send in late ones. I don't have time to wait on you. It's not fair to me and everyone else.
The first and last lines should be memorable and are the most important lines with the exception of the name of the product (if it is a commercial). Start strong so they will pay attention. Finish strong so they remember you. And make CHOICES. What is going to set you apart from the 1000 other VOs they are going to listen to?
Comedy scripts should be zippy, drama should be deliberate (not Shatner-esque). Make your pauses count. Pay attention to the intended length of the spot and keep an eye on your time. Most spots are laid out in 15 second chunks so it will be either 15, 30 45 or 1 min long. Figure out the length of the script to anticipate the pace of the script.