I've been subbing since 2000 at the same elementary school in Plano where my daughter attended.
Fortunately, I know most of the students so I have a some upper hand because I know parents due to being neighbors, bunko, social, etc.
Most teachers, at least where I sub, have detailed plans. If not the weekly plans are available and I just follow them as best I can to keep the students on track. Believe me...the teachers are thankful you are there to keep control in the class. I am in this school enough to keep me busy 2-3 days a week and I am not looking for that much so I know the routines and schedules so the teachers mostly let me run the class according to the plans for the week.
DO NOT BE AFRAID to show control EARLY on so that kiddos know you mean business. Example.....I knew I was going into a class where subs hated to go back in Oct. I went in with "tickets" and a drawing for the end of the day. My deal was OK'd by the staff BEFORE I started. I gave tickets to everyone as they came in... as the day went on... IF needed I gave an extra ticket to those who showed most responsibility, etc and I took away tickets from those who needed it due to behavior. Whatever you choose... I have used a couple of tactics...it works.
Once you show the control of giving recess time out or whatever is needed.... you will get the attention of the class. ALL classes have a couple of kids who will test you and unfortunately...even if you know the parents...you need to follow through as teacher..not as parent friend.
You can do it and it can be rewarding.
IF I have an issue, I just ask "how is your mom, I have not seen her in a week or so, I can't wait to catch up with her" and that child is NO LONGER an issue.