Find out beforehand what the meeting is about. Think through your viewpoint. Be prepared for the impromptu situation. That's what distinguishes us in life.
Use the speak-on-the-spot format to organize those thoughts. It will make your comments - and you - more impressive.
Be a physical presence. Sit up straight, speak up, focus on one person at a time when speaking. Save the slouching for later.
Seize the opportunity the meeting provides. Be a mover and shaker. You are smart enough; you know how to do it. Why let others steal the glory?
Start with your viewpoint. Instead, start by rephrasing the subject. It gives you ownership of everything that follows.
Think you can wing it. Spend the time. Prepare. Do it right.
Drone on. Sixty seconds is plenty of time. Your goal is to contribute, not to bore.