Prepare one question before you walk in

It is much easier to speak when you are not inventing the sentence on the spot. Before a class, read the slides or notes for ten minutes and write down one thing you do not understand. Before a meeting, look at the agenda and write one question.

Write it in full: "Could you explain why we use a hash map here instead of a list?" Then your only job in the room is to raise your hand and read it. Over time you will need the notes less.