I know you are excited! About 15 years ago, I did a long-term maternity leave for 9 weeks in fourth grade. It landed me a full time teaching position in fourth grade the next year!
Just like the other post said, I'd check with the teacher about what things she already has in place. In my experience, I continued what the teacher had started. For example, the classroom rules, marble jar, etc. were left the same.
I wish you the best of luck. I teach fourth grade and I love it! Let me know if I can help you.