Your teen should also walk with two or three references in hand. They can be from a teacher, a former boss, a coach, a baby-sitting client -- anyone who can vouch for their maturity and personality. Walking in with these references will show the prospective employer that your teen has a track record of responsibility and is taking the position seriously enough to come in prepared.
You can help your teen with practice interviews, either with you or a family friend. Teens must be able to talk about themselves, why they want the job, their experience, etc. They have to be able to communicate that they want the job for more than just the cash -- they want to get something meaningful from the experience. This tells employers that they won't just take the money and run: They will approach the job with respect and dedication.
Another key is flexibility. Every teen wants nights and weekends off, but they will have more options if they are willing to work some of the less-attractive shifts.
Don't wait for the phone to ring. When your teen is at the interview, he or she should should ask what the process is and when a decision will be made. Your teen should be persistent without being a pest -- check in once a week until it's been filled or they've been hired.
Tory Johnson is the workplace contributor on "Good Morning America" and the CEO of Women for Hire. Connect with her at www.womenforhire.com.