It just so happens that I made this exact same switch in my career... about 30 years ago! (I'm now retired) High school and middle school behaviours are different kettles of fish but there are some general strategies that are applicable to both.
I found it useful to create an image in my mind of what my perfect classroom would look like: what the students were doing, how they were interacting, what I was doing. This image would guide my decisions for anything that came up in the classroom. For instance, I envisioned every student feeling safe and willing to contribute to the class so I dealt firmly with any teasing, bullying, put downs or inappropriate jokes. The overall goal is to create a consistent environment that is conducive to teaching and learning.
Being prepared is important because fumbling around during a lesson will bring out unwanted behaviours. I found that backward planning – where you plan the end results or outcomes of your unit first and design lessons to get you there – helps you see what comes next and lets you deal with unexpected troubles or interruptions quickly. So, if the internet goes down and today’s lesson is trashed you will have a follow up lesson in mind already.
With high school students you will get more adult behaviours – good and bad. I have found that they will respond better if you treat them as adults. Non-verbal communication will tend to work well for most. Rather than group discipline, I would deal directly with a student for their misbehaviour by having a one-on-one conversation with them (usually outside the classroom door). I would remind a disruptive student that if they wished to be treated as an adult then they must behave like one by showing self-control. So, consider how you would want to be treated if you messed up.
Hope this helps!