It's not about yelling. It's about holding guys accountable and demanding excellence. You also have to have some credibility to do that, so as a first time or young coach, you need to work hard to earn that trust and respect.
I was watching the "Football Life" show on Jimmy Johnson recently, and he said something that made sense. He said that as the head coach, when you walk into the building, you need to make sure that you are able to touch everyone in the organization, and let them know that you recognize them, and are watching them, and be able to motivate everyone from the QB to the backup guard to the guy breaking down film to put in that extra effort to reach excellence. He also said you treat everyone differently, and there is a lot of psychology involved.
That's why I think it is hard for a coach to come in and double as coordinator as well, because the coach needs to spend time motivating those around him to produce at a high level, and display that there are consequences when you aren't cutting it...