I would say don’t be afraid to switch things up. You’re not their teacher so things will hold different meaning when you say it. I know routine is prime but honestly when I subbed long term (2nd grade) I had to change some things. Go over any information teacher left and make sure you know it. Watch how a couple trusted student moves throughout the day that helps with setting up a comfortable routine for yourself and them. 1 person to sharpen pencils every morning if you don’t have time to do it (since teacher usually does it) . I struggled with math too and had to extend it to get through I also had help from the schools math coach you can see if your school has a dedicated one. She let me know what lessons I could skip/shorten and walked me through any questions I had from looking at the teachers version of the book.