If this is your first time registering for classes, then I'll tell you now and say that you shouldn't take any advice but your own. (Kinda ironic that I'm giving you that advice huh)
Anyways, most schools have advisors that tell you what classes you should or should not be taking. Well, take whatever they give you and shove it in the back of your brain because they're wrong. Well to an extent. Your advisors don't know your learning capabilities, and they always push you to take certain classes that may or may not be too hard for you. I took a math class that I thought I was prepared for, but turns out I wasn't as prepared as I thought I was. I ended up failing that class because I had no clue what was happening. Calculus is the enemy.
Whatever you took in high school, take the college version of it instead. Instead of going straight to calculus or whatever, take college algebra (precalculus) and work your way up instead. Not only will you have an easier time adjusting to college difficulty, you'll get a refresher on things you may have forgotten over the summer. If the class is to easy for you, then good for you, you just got an easy A class! Woo!
Always ask people if they took a class you want to take. This person will give you a good insight as to how difficult or how enjoyable a class may be. We have a class that's nicknamed Dirty 230, it's a Human Sexuality class that you learn a lot in, AND its an easy A. Fit in one of those easy A classes in your schedule every semester to help boost your GPA. For me, most of my easy A classes are within my major and minor. So if you already have in mind what you want to major or even minor in, ask around for those type of classes.
Ratemyprofessor is the holy grail. If you don't know anyone that took the class you're about to take, look up the teacher on ratemyprofessor.com and see how other students did in that class. However, sometimes you may get unlucky and get a professor who isn't actually a professor, but a grad student instead. Well, most of the time, they should be easier since they're students too essentially. If you have the option of two different professors, always choose the one will better reviews because chances are, you'll feel the same exact way. Choose the professor you know you'll get a decent grade with.
I don't know about you, but there are a lot of courses that I have to take in just one semester, and because I'm a science major, I always have a lab. To make things easier for me, I always use an excel spreadsheet to figure out the best schedule for me.
As you can see, I set my classes up so that I have options. In this case, I don't know if I'm going to pass the first semester of organic chemistry. So I work my schedule in ways to accommodate for the chance that I may pass organic chemistry to take the second semester of it. I'm banking on that I do, but if I don't, that's okay because I have a Plan B. Always have different options for yourself in case the class or section you want fills up right away.
If you're a science major, this will definitely help you to see what labs will fit where. This method works the best for me.
Remember how many credits you're taking this semester and ask yourself if you'll be able to handle it all. My schedule may seem crazy, but because I fit in couple breeze classes, it shouldn't be too hard.
Always keep an eye out for the classes that will bring you dual graduation requirements credits. One of the Biology classes that I might be taking (if I retake O. Chem I) is what WSU calls a Tier III class. By taking a bio class that is also a tier III, I'm killing two birds with one stone with my graduation requirements. This allows me to take fewer classes in the long run. Always look for ways you can do this.
Always stick to your gut and know that if you don't like the professor of a class, drop it. Or change to a different time. Don't allow yourself to suffer through a class where the teaching style of a professor doesn't work with your learning style. A lot of times this will happen, and sometimes you can't avoid them. But if you can, do so. Do it quick. Use the first week of classes to test the waters, and if you don't like it, change it.
I hope I covered enough on registering classes, and how to avoid failing and falling into academic deficiency. A lot of things as simple as registration has to do with the outcome of the semester, and your success. Once you find the best ways to do certain things, the stress of classes for the next semester won't be so bad. Hope you keep this in mind since it's never too late to change your schedule for the next semester! Good luck!