How do you NAIL a commercial audition?

I have gone on several commercial auditions before and only gotten one as an extra, and it was mainly because of my red hair standing out. I am a good actress, I have been in professional plays and got a small role on the Hallmark Channel, but I can never seem to get commercials! Don't get me wrong, I am very grateful and I realize some people go on HUNDREDS of auditions before getting a small role or an extra, but could anyone give me some tips? I only have one line. It's, "Mom, Adam didn't eat all of his food!" and I am saying it like I am tattling. Do you have some tips for me? What do commercial directors look for? I have a good look for it, I believe, and I am a pretty good actress, I just need to know what they usually look for. Thanks!