Even a simple “hello” can be an occasion for a mini-lesson in an ESL class. The teacher can tell students after they’ve greeted each other that Americans rarely greet each other with “Hello”; “Hi” is more common, and “How are you?” or “How’s it going?” more common still. This can also lead into some discussion of the true meanings of these expressions. Unless it’s from your doctor, “How are you?” is not a real inquiry into your health but just a greeting, and the appropriate response is “fine.” Teachers should also go over correct pronunciation of the expressions: in phrases like “How’s it going?” typically words are reduced and connected, not pronounced individually, as it is written, and “How’s it” sounds something like “Howzit.” Additional expressions for greeting and expressions for farewells can also be gone over if time.
This is an effective warmer because it takes what students are likely doing at that moment, greeting each other, and turns it into a lesson on idioms, culture, and pronunciation.