Have clean UI. Throw in some edits. Either be silent, or talk nicely. Nobody wants to hear autistic screeching when a person fails a defile. Don't beg for likes and subscribes. I don't do it because I'm asked to, I do it if the content creator uploads videos that I like. ALL CAPS TITLES ARE DISGUSTING. DO NOT DO THIS. NO CLICKBAIT titles or thumbnails, they are just so damn boring and can drive off viewers.
My go-to WoW video (music + VO combination) as an example. Loudness warning as Algalon dies.