Cover is really tough, I’ve worked in my school for 10 years and even know when I get called emergency cover for some reason the kids try it on for a mo.
You need to be consistent, and follow the school behaviour policy to the letter. Never deviate.
Ours is warning 1, move in room, send to a different class with other kids- the latter results in a call home and detention.
Read up in your school policy and use it every single time you need to.
Learn the kids names, I know it’s hard in a big school, work out who are the students you defo need to get on side, those with needs etc
Does your school use seating plans?when we give our cover work we need to send in our seating plan, which has any needs on it, their target graces, CAT bands etc- you could ask SLT if this could be made a policy as would help all cover supervisors.
Call parents/carers , email tutors, email Class teachers, follow the policy.
Be consistent and it will pay off.