You have to have your own tricks as a substitute teacher. Don't ever let the students believe for one second that you don't know what you're doing. Arrive early to get oriented. Make sure you know the lesson plans front to back. Talk to the other teachers, if possible, to find out if there are any systems in place for discipline.
I learned to keep a watchful eye and not allow students to get away with things that I know are against the rules - like texting or listening to music.
But at the same time I've learned to be relaxed. Sometimes, as a substitute, you really don't have much control or say over what the students can and cannot do. You are there to monitor, not discipline. So sometimes you just have to go with the flow and just try to keep the noise-level of the classroom down to a minimum.
The hardest thing about substituting is knowing you don't have much control. Many teachers don't let substitutes present new material or even review, so it's often just busy-work and the students know it. They assume the substitute doesn't know anything. The worst part is not knowing their names or who they are. If it's your first and last day in that classroom, you don't get the opportunity to really learn names, so if a kid is acting up, you can't call them out by name and put them on the spot. They know they are relatively anonymous, and there is power in that. It's frustrating.
The best part of substituting is getting to see all the different campuses and the different systems in place at the different schools. Every school has it's own atmosphere, student body, level of teacher enthusiasm, resources, etc. It's definitely fun getting to be a part of so many different learning environments.