Public speaking is the #1 fear. [My opinion is that spiders are worse than public speaking.]
Acknowledge that fear of public speaking is normal.
Encourage your teenager to practice, practice, practice!
Choose a topic that is familiar to him or her.
What is the style of the speech- persuasive, informative?
Preparation includes being well-prepared, knowing the audience, saying the speech to as many people (and patient dogs or cats) as possible before the presentation.
Practice in the mirror or on video.
Use a digital taperecorder to have the person hear what he or she is saying.
Speak to the audience. Eye contact is important.
Communicate to be understood.
I would also encourage the college student to find speakers that he or she likes and watch them on You Tube.