Congrats Banshee

As a former Instructor in the Army (average Trainee class size 156) a bit of advice.
Always be an expert in the subject at hand.
Every class will have what we called "Sharpshooters".
They're the ones in class who will try to make you slip up/test your knowledge
about whatever you're teaching or discussing.
Every day you can learn something from someone, regardless of age.
If you mess up and get dates, chronology or whatever wrong, correct yourself
as soon as you can. Admit to making a mistake and correct it.
The students will reward you with respect and admiration.
Get to know each student.
Make sure they know that you're approachable to help them as needed.
Best of luck with your new career.

Oz