Here are five simple ways to get a better grade.
1. Read your syllabuses & write down important days! (e.g. when a test/quiz/exam occurs)
2. Keep a folder or a notebook for a specific class. Try color coordinating the notebook and folder. It'll make you seem and feel like you're prepared for classes.
3. Make friends in all your classes. They could get you notes when you miss class. You can also have someone to study with, too.
4. Introduce yourself to professor/teacher. They'll be more likely to help you if they know you're a good student. Plus, they could be more willing to bump up your grade if they know that you actually care about their class.
5. Study every day. It'll help when it comes to exam time. You won't be like "when did we learn this"
I hope these simple ways help improve your grades.