Make sure that you present your rules and expectations to the class at the beginning of the year and after long breaks to ensure that students know and understand them. In addition, give reminders frequently in the beginning as they are learning.

If students break any of the rules or expectations, just start off with a verbal warning  for first time offenders. 

If behavior continues, give discrete gestures such as touching their desk or standing by them to send a message to change their behavior. 

If the subtly redirection does not work too, then consider sending them to the hallway or to a safe seat and have then fill out a reflection form to help them reflection on their actions to improve them in the future

If all else fails, get their parents or principal involved to help you with some diciplimnary actions for their bad behavior and disrespect.