That’s a great idea, shadowing in the medical field. It’s a nice way to open your eyes and your mind to this profession and to see if it’s something you’d want to work for.
I can’t think of anything you need to specifically do to prepare. It may be good to have questions ready to ask the nurses you see. Once you think of some from now until you start, write them down! That way you can get the information you want and not forget to ask. I’d say before you start, have a good night’s sleep, eat a great breakfast and keep an open mind. That way you’re alert to everything happening around you and you can absorb it all.
Good luck in your shadowing and hopefully we’ll recruit you into our world!