Using Your Phone During the Interview
Before you get to your interview, silence your phone. Texting during your interview is not only rude and disruptive, but it's a pretty clear message to your potential employer that getting the job is not your top priority.
For the same reasons, don't answer calls (and certainly don't make them) during the interview. To resist the temptation to check your phone, stow your phone in your bag before the interview. If you accidentally forget to turn it off, resist the temptation to check it if you get a message or call.
Not Paying Attention
Don't let yourself zone out during an interview. Make sure you are well-rested, alert, and prepared.
Getting distracted and missing a question looks bad on your part. If you zone out, your potential employer will wonder how you will be able to stay focused during a day on the job, if you can't even focus during one interview.