When there's a natural pause in the conversation, when silence falls and something needs to fill it, when people are looking at you, expecting you to say something, anything, when making polite noises just won't do. Pace your delivery. Speak at normal conversational speed, possibly even a bit slower. Breathing paces speaking, it limits how fast the words come out. Find your own natural rhythm.
Timing is critical.
Modulate your voice. The circumstances will determine the optimum loudness. Soft, but clear, gets attention. Enunciate, but do not overdo it. Keep eye contact and smile.