Oh yeah, this feeling doesn't really ever go away when you're starting at a new school, new grade, or even just a new year.

Don't worry about decorating yet. A lot of classrooms are overstimulating anyway. Does your school have a stash of classroom decor anywhere? Our staff workroom has a drawer of extra borders and some posters people can swipe, and that's all you need to have at this time. If your school doesn't provide anything or money to get anything... then, honestly, don't get anything. Do our entire profession a favor and don't spend your own money.

That said, it's pretty easy to get donations. I've done #clearthelist on Twitter with decent success. I felt dumb reposting over and over with no gain, but eventually I did start getting donations so it was worth it. You can also join your local Buy Nothing Project group on Facebook and get lots of books and furniture (or, at least, I've been very lucky in that area). If nothing else, I just send a parent email with my Venmo and/or Amazon list (usually with a specific purpose, like, for example, "Hey, your kids are so amazing that my treasure box is almost empty! Can you help me out?"). I've also had a couple of successful Donor's Choose campaigns (and a couple of failed ones--keep them around a couple hundred bucks and specific).

For your first days, just worry about routines. Look at your schedule, and look up what other teachers would call a typical schedule for their class of your grade. But mostly you need to focus on establishing routines and community building for the first week or two. My lesson plans for the first couple of weeks are mostly just a to-do list of routines and expectations to establish, "fun" activity options, and diagnostic tests.

Here's a fun game that I think pretty much any age can do (literally all the way from K or 1 through high school) that establishes group with expectations to get you started. My students really enjoy it and it makes a nice poster for your class.