2. It's okay to make mistakes (and you will make many).
One of the hardest things for me to deal with when I started teaching was how new everything was. I was teaching concepts in science and social studies that I hadn't encountered in a decade, and as much as I worked to learn all of the curriculum before teaching it, I was pretty overwhelmed. I can't tell you the number of times that I misstated a fact or explained something incorrectly and had to go back and correct it the following day. For a while, I was really frustrated with myself. I had been working so hard, and I felt like it still wasn't enough.
Accept that feeling. Embrace it. We tell our students that it's okay to make mistakes because that's how they learn. The same is true for us as teachers. I don't think there's ever a moment where you feel like you've done everything you could possibly do to plan a lesson, learn a subject, or help a student. There are so many demands on your time and never enough hours in the day. Do the best that you can, and learn to be at peace with that. There's no such thing as the perfect teacher, and you'll have a pretty disappointing career if you make that your goal.