Your first class (or even first 20 classes) isn’t the time to show off. Keep it simple and stick to postures you feel super confident explaining. This will make your job a whole lot easier.
If you play music in class, make a playlist of songs you love that match the vibe you’re going for. In the beginning, my playlists felt like a security blanket. When I’d hear a favorite song come on in the middle of class it helped calm down my nerves.
Your first class won't be perfect and that's OKAY! Whatever happens during your first yoga class cut yourself some slack. It’s not going to be perfect but don’t beat yourself up for every tiny hiccup in class.
Find the joy in what you are doing. Something changes in your voice when you smile and your students can pick up on that!
The more you teach, the easier it will become. You'll start to figure things out like what cues work for you and what your vibe is, It gets easier. But you gotta start somewhere!