The course that was the biggest surprise to me was probably MATH246, Differential Equations. This course was probably the hardest math course I've ever taken. I know that sounds like a weird answer, but MATH246 to me felt... different than every other math course I'd taken. This was the course where it struck that I was in college, not just an extension of high school courses. MATH246 was the first course where I truly felt like I was out of my league. No more baby things. Now we're doing real math. Personally, on the point of "what strategies might incoming students pursue to experience similar surprises?", since it's a distinctly bad surprise, I wouldn't really suggest incoming students to pursue that kind of surprise, but if it's required for their major... I'd tell them to watch out.
I didn't establish very many large relationships with professors. It's kinda hard to talk about this topic because, well, I'm not the most experienced at it. I didn't go to office hours, I was generally pretty quiet in my classes, and I didn't send many emails. My advice to incoming students to develop relationships with their professors would be to do all of the things I didn't do.
It's nice having motivated friends to help with lack of motivation. Even if you're with someone else who has no motivation, the simple act of having someone next to you can help motivate you to focus and complete your assignments. Having friends that can help with that was what helped me survive my first year of college. With great freedom comes great responsibility, and managing that responsibility was a hard adjustment to make, and one that was helped greatly by my interactions with friends. My advice to incoming students would be to surround yourself with smart and studious people. Talk to random folks in your classes, make friends or acquaintences, do all of that, and you'll be set. Surrounding yourself with those kinds of people will help you overcome motivation problems.
In retrospect, I was prepared for NONE OF IT. High school is way different from college. High school is quantifiable, measurable, regulated; college is not. Freedom is college's biggest strength and greatest weakness: you have time to do anything, but what will you spend that time doing? My recommendation is... I don't have one. To be honest, this is something you have to learn on your own. Prepare yourself with learning about focus strategies and stuff, but expect the absolute worst. There's not much you can do to get yourself ready other than mentally steel yourself to the prospect that anything can happen.