First and foremost is research. When signing up for classes, research what classes you really need. If you're trying to get a transfer degree like me, study which classes give transfer credits. Know what classes you need to take. Second, look at every possible time and professor for that class. Ratemyprofessor.com is a great resource to research how good teachers are. You're taking a big chance if you sign up for a class with a teacher you know nothing about. If I have any choice, I don't sign up for a class with a teacher whose rating is less than four out of five stars on that site.
Second, if your schedule allows for it, try to set up your classes in a way you can manage. If you're going to take four classes in one day, give yourself time for a lunch break and homework catch ups. Seems like common sense, I know, but if you're anything like me you'll be too enthralled by the fact that the time slots fit perfectly to think about the logistics.
Third, for actually succeeding in class, sit in the front and make friends with smart people. If you're in the front it'll be a lot easier to pay attention (and a lot harder to fall accidentally fall asleep, if you're me) and if you make friends early you'll group up with people that actually do work. If you exchange phone numbers you'll also more than likely be able to collaborate on homework and stuff if you need it, too.
Lastly, as I've already explained recently in a previous post, never stress out about something that you didn't get the chance to put all your effort in. At no point will you ever be the only one to have crammed in that essay in an hour last night, and expecting a terrible grade because you did is silly. Even if you're in the minority as far as preparation goes, any effort at all will get you the points you need to pass a project. But not having enough time is never an excuse to skip doing important assignments altogether. Fifty out of a hundred will always be infinitely better than zero out of a hundred.
Mostly, don't overload yourself. In general when you're trying something new set a low bar for yourself until you know how much you can handle, then push that. If you sign up for an 8am to 3pm schedule because that's what you did in high school, you're doing something wrong. I'm not entirely sure why, but you will die if you do that. High school is in a lot of ways easier than college, but college is better as long as you know how to handle it.