Depends who your audience is. If it's around middle school or highschool age, do something interesting that will keep your audiences attention. For example: A magic trick. Bake cookies. Pack a hiking backpack. Put on ski/hockey/football gear. Draw. How to tie a tie. How to sell something on ebay. How to jump a hurdle. Positions for dance/ballet. A card trick. A dance routine. Playing the drums/piano/guitar/violin etc. How to study for finals. How to make a demonstration speech. How to make a speech. How to survive teacher's lectures. Getting people's attention. Etc. You can pick anything and make it last up to 3-4 minutes, just by giving history, giving step by step, and explaining each step for a few seconds.