tldr: Preparation, patience, repetitiveness, and don't use calculators
I think there is at least one high school teacher in this board. I tutor introductory college classes (calc and physics) to college students for the past three semesters. The sessions I have could be taught at a high school level (I took em in high school with little difficulty) and college freshman still have that high school sass.
The biggest thing for me is being prepared. I scored 5s on AP calc 1 and 2 but the kids I tutor damn well can get me flustered if I do not come to a session prepared with problems, answers, and full explanations. If you're doing problems yourself for fun, you can wing it. But if you expect 30 people (3-4 in my case) who have never seen it before to understand it, you need to know every example you give like
Next, I say the same damn thing 3-4 times a week for an hour at a time, minimum. Minimum because you'll have people who won't take notes and they'll only ask you about whatever you said next week when it bites them on the ass in their homework or quiz. HS teachers probably get that scaled up to 3-4x/day.
You can't ever show kids negativity. You're getting paid to explain this shit, and it's the first time they've seen it in their lives, so be cool. HS teachers lose all credibility when they flip. You in particular will go from "hot muscley math teacher" to "roid rage hothead". Encourage questions like:
"What's the difference between a volt and a charge?"
"So you take cosine of the force?"
"Polynomial? What's that mean?"
Think back on the classroom experiences you've had in your life. I had a teacher that befriended our class and the semester finished with an 80% average. This class I'm taking right now, the teacher laughs in your face for answering something wrong, (which I think is kinda fun) but the class is averaging 60% on quizzes. These classes are about equal in difficulty with the concepts given.
As a final remark, really consider making your room a no calculator zone if applicable (I assume you're talking about physics or chem, maybe you're talking about earth science or biology). Calculators are safe because you can distract yourself from button pressing and forget for five seconds that you don't know what you're doing. Force your kids to think in terms of variables and substitutions and how units interact and cancel. Whenever one of my tutees is stumped, they're slouched over their calculator and their sheet for scratch work is empty. Then I have them write out variable for variable what to do, and all of a sudden they have it right.
Edit: Oh oh oh. And if some smart little punk asks you the ole, "When will I need this in life? I want to do X", I always answer with, "Because if you can't figure this out, I don't want you working on my missile launcher, or my tank, or my airplane, or my car." Simple answer that just works nice time after time.