Like everyone said, networking is crucial. You never know if a classmate might become super helpful in a class you struggle in, or if they can hook you up with a job or something of the sort. Actually got an internship from a friend I met in a class.

Of course, this doesn't just apply to students; this also applies to faculty. 0_o
Try to get to know your professors, whether it be during office hours, after class, or even over a cup of coffee. See if your school has some sort of dine/coffee with a Professor program.
Not only will it make a professor less intimidating, it will also make them more willing to help you out since they'll see that you're putting more effort into their class. You'd be surprised what can happen from simply going to office hours often or inviting your professor for lunch. I personally scored some letters of recommendation and a job simply from this.
Time management is also important.
One does not simply procrastinate in college.

It WILL bite you back.
Also, if you find yourself struggling in school, don't take it too hard upon yourself. You most likely won't be the only one that feels that way even if it seems like it. While you shouldn't be settling for less, you should not let lower grades discourage you from staying in school. Rather, look at it as an opportunity to improve upon your study skills or time management.
Most schools will have a resource that you can tap into for additional help. It varies from school/classes, but there's anything from having friends in the class, talking to the professor, talking to the TA's (if your school has them), going to the lab or dedicated help area for the department of the class, etc... Again, talking to your fellow students can be very helpful here because some might know things you don't.
That being said, even if your GPA isn't where you would want it to be, you shouldn't worry too much about it as grades aren't everything. You should also be looking into getting an internship as soon as you can. Employers typically like seeing people that have actually had some experience in the working field since you can only learn so much from books. Find a balance between doing well in school and gaining experience, and you should be more than OK in school.
I think everyone else here did a pretty good job with the other advice.
Me? I'm going into my senior year. (my school's on a quarter system) Studying Computer Science with a Specialization in Bioinformatics.
Trying not to rush through college though as I prefer to gain as much experience as I can and keep my grades up. Better to have that and finish college late than to graduate early/on time and have meh grades and work experience.