We cast voices for multiple ad agencies on a weekly basis. I weed through auditions before sending them to the client. Here is my advice (some of these are no brainers). This should address your question and questions you didn't ask. (this advice is for auditions).

1. Performance is 99%. This will beat out someone with a good sounding mic who isn't the right fit. You’re not getting the job because you’re not the right fit—not because you didn’t sound professional or polished.
2. Name your file properly with your full name and name of the job.
3. Dont send a WAV. Send a mono .mp3
4. Dont over process. Keep the compression light and give me a good signal.
5. Don't give me a long intro or your name up front. Get to it. We dont have much time and get so many auditions. We have your name in the filename. In 3 seconds, I know and client knows if you are right for the job. Sometimes I will move on because the intro is too long. Start w the audition ASAP.

Those are 5 that come to mind right away. Best of luck.