Yeah that's tough. It's going to take practice, but if you trust your brain, it will come up with a proper response in the moment. It just needs the space and flexibility to process the other person's words and then form it's own words. Clearing your mind like that is hard, but you can practice it with meditation. (Meditation has done wonders for me on many levels) And start small. Try this focus with close friends or family first. And remember it's okay to pause for a moment before you respond. I'm sure that gap of silence is longer in your perception than in reality.