Relief Teaching is hard enough without making a complete mess of it. The last thing you want to be known as is a CLUTZ! Spend a little time learning how Not to make a mess of relief teaching.
There will definitely be times when you need to call someone for support. When relief teaching, you might need the support of others. But you should exhaust all other options. When relief teaching, each time you defer discipline to others, you reduce your authority status with your students. So don't do it very often.
2 - Complain about your class to others.
No one likes a whinger. When you complain about your class you are saying that you do not have the skills to manage ALL OF these students. How different would the conversation be if you mentioned how GOOD are some of your students.
That sends the clear message. Staff know that you get a day's pay. You just don't want to send the message that you are in it JUST for the money. And while that might well be true, you are also there to value-add to your students.
Most teachers will welcome anyone who is relief teaching to their school, but you should take the first step and introduce yourself. These are the people who will be telling the boss how you went. They will also be your first call on matters of procedure. Build a warm relationship. Successful relief teaching is built on relationship.
Always pack your own cup/mug and your own coffee/tea bags. Better still, leave your named cup at the school so you can use it when you are invited back. That sends the message that you really want to come back. Perception is pretty important if you are relying on relief teaching as a paying proposition.