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If you need to open your mouth during an interview, every word you say should be gold. Don't fluff or speak without objective. Speak with a purpose. People are going to judge and there very little time you can make the impression you want to give.
When you say less, each idea you express holds more weight.
Pause more often
There is value in silence. Slow down so the other end can understand what you are trying to say. You may have an accent. You may be nervous and fail to articulate or enunciate your words clearly. Mumble jumble sucks when you need to decipher things.
Control the conversation and guide it to a topic you can handle well
Interviews are all about conversations on topics either party is interested in. So if you can nudge the interview into a certain direction you are more familiar with, have practiced for or at the very least, divert away from difficult topics, that's a win for you. Talk about things you can handle. Also relieves stress in the interview.
Warmup with other interviewees
In the waiting room, talk to your competition. It can be about anything, not just about the interview itself. The dialogue you strike up helps you warmup your brain so you can better cook up your thoughts later. Also the warmup is physical stimuli for your facial muscles. As you start moving your jaw, wagging your tongue and vibrate your lips, you kickstart your mouth.
Your brain gets switched on. You mouth gets fired up. Great. All good to go.