What would be good techniques to call my students attention towards me?

I have realized that when teachers try to get students attention to say something, it normally doesn't work. So, other than saying, "class look up here," what would be good techniques to get them to quiet down, listen and focus on me?

What would be some good activities to get all students involved and participating?

How far would be too far (or crossing the line) for a teacher to keep a class under control that is constantly getting into fights and/or arguments?