Everyone says don't pre-study, and while I generally think that is great advice, I constantly found myself thinking during my first block that my life would have been a hell of a lot easier had I put in the effort over the summer to learn the major metabolic pathways (glycolysis, gluconeogenesis, glycogen storage and breakdown, lipid metabolism, TCA cycle, amino acid biogenesis and catbolism, etc) cold. I spent so much time just trying to re-learn the basics that I struggled to find time to study the actual metabolic diseases we were learning about. So if someone really wanted to study, that would be my advice. Don't try to memorize every nerve, artery, and vein in the human body, but your life will be a lot easier if you already have a firm grasp on basic human metabolism.
Other than that, if you struggle with confidence issues, anxiety, or depression, do whatever you can to work on those. My confidence issues have been a huge detriment when I'm expected to come across confident during patient encounters and I just don't.
I don't think there are too many other things I could have prepared for until I got here. Doing things like finding time to clean my apartment and take care of myself when I feel like everything is go go go at school all of the time has been a struggle, but I couldn't really prepare for that ahead of time since there was no way to place myself into the pressure cooker ahead of time.