Hi! I'm not an experienced teacher, but I am currently shadowing a teacher for my licensure and degree requirements. I thought I would share what she does in the classroom because I think it is great.
She has a quote up on the board that says listening helps me learn and learning gives me knowledge. She often reviews this at the beginning of her lessons with the whole class. She will start the quote and then ask them to finish each part. This gets everyone focused for the lesson. She also has a board that says 'give me 5' and it asks the students to pay attention with all of their senses (eyes, ears, mouths, brain, and body). She will review this at the beginning of a lesson or in the middle of a lesson if the students aren't focusing.
I am also taking a class right now that emphasizes the use of phenomena driven science instruction. I think this could be a great idea for a class you may not have a lot of rapport with because it is a fun and interactive lesson. You could have a poaster board with rules at the front of the classroom so the students are safe and respectful and go back to them if they are not focused.