In a previous tip I gave pointers on how to look over your shoulder without veering into traffic. If you need to look over your left shoulder drop your right elbow. This is a very subtle way of steering your bike.
I find that most new riders steer with their shoulders or wrists. There is nothing wrong with doing this. But what if you want or need to be more subtle.
If you are in a peleton with 100 other riders you will quickly feel cramped. You still need to steer even though you are now handle bar to handle bar. So if you need to steer left drop your elbow slowly and hold it long enough to put your bike where you want it. If you pull your elbow back up quickly you will return to the line you were riding.