It would help to know what you ARE doing... For example, one of my bug-bears as Professional Mentor is when there is low level chat and the teacher just talks over it. Most of my trainees get fixing that as a target at some point, and my approach is this: "Right, eyes on me. Mouths shut. Stop fiddling. Eyes on me. Thank you" WAIT for total silence. If I am interrupted even the minutest amount I stop, mid word if needs be, and fix the offender with THE LOOK (I had a student once who told me I had evil eyes. I took this as a compliment) and say "Thank you, Bob" in a tone that promises suffering. I can keep this up for a long time... and the rest of the class usually get annoyed with Bob and tell him to shut up! I simply WON'T be talked over... never have, but I also have a vocal cord issue which means raising my voice is only for emergency use.