I work at city schools. Discipline is easy. Put yourself in their shoes. They snap at you, you gotta snap back. You can be that good friendly teacher they've never had but don't let them back you up into a corner. Let them know who runs shyt. Don't be scared to write them up. Write up 5 students at a time if you have to. They'll all fall in line within a week's time.
I was tested my 1st day where a 5th grader said "oooh this bytch bout 2 get fired" lil mama was in peak for 3 days straight.