"Calm down" is a phrase that we all use, especially with kids when experiencing intense emotions. Here are some alternatives that might help resolve a situation quicker and more calmly. Gentle parenting.
In order to establish control before beginning instruction, students need a way to stop what they are doing so they can listen out for instruction. I envision myself using different strategies, such as having students stop and put their hands on their head, clapping patterns with my hands, and counting down from five to establish control of the class before I begin instruction. This will manage the classroom by making instructions clear and saving time by not having to repeat directions.