Slow down, breathe, and don't be afraid of stopping talking to think or take a sip of water.

Nervous speakers feel the need to fill silence with filler words (umm, err, etc), or will ramble on quickly with their speech.

Confident speakers will embrace silent moments and allow them to exist naturally. In fact, allowing moments of silence can be very useful because it gives you a chance to take a deep breath, or to have a quick sip of water, or just collect your thoughts, whilst simultaneously giving your audience chance to digest your words and reflect.