The video is excellent and I would encourage anyone reading this to watch it, but for the benefit of those who don't like clickbait the answer is: surround yourself with a quilt, jacket, pillow fort, or similar, because although it looks ridiculous it gets rid of background noise and muffles reflected sound.

(I haven't "saved you a click" because you should watch the video anyway. It's not just about how to get better sound when recording or broadcasting. About ten minutes.)