As someone who has stood in front of a class room in Florida and delivered my own 5 minute talk, and watched a class full of others do the same, I can offer you some advice based on the feedback we were given.
Firstly, pitch the talk to your audience's level, ie. nearly CFI's - don't dumb it down or overcomplicate it. Next, use some humour - most of these talks are on relatively dry subjects, so think what would keep you interested? On the same theme - visual and sound effects work really well especially with powerpoint, I'm sure you've heard about great presentations in the past there. Keep to your five minutes, don't ramble. Make eye contact with everyone in the room, as it keeps their attention.
Finally - the more you can practise and memorise what you're going to say, the more natural, conversational and engaging it will be.
Good luck and enjoy it - most of my class did!
