Ask HN: How to Speak Confidently?

How do I learn to speak confidently in a group setting ? Sometimes when I start speaking and if people are silent or if I can not read their expressions, I start loosing confidence. If someone interruptus and start asking questions or criticizing, I loose my train of thought and start second guessing my ideas and opinions. I start to avoid participating or stop presenting my ideas. This is stopping me from growing in to a good engineer. How do I get better ?