What is a bad professor? We've probably all had at least one, and we know them when we see them, but what exactly makes a professor "bad"?
Firstly, just because a professor has a bad reputation does not make them a bad professor. They might teach an inherently hard class that everyone struggles in and then blame these struggles on the professor. Before you make the initial judgement that someone is a bad professor, take a class with them and decide for yourself.
But I'll tell you one thing, if you're sitting in class and you consistently feel the urge to sleep, leave, or die, you're probably in the presence of a bad professor.
For starters, professors who seem too involved with themselves usually aren't the best. If they can't project their voice to the class, or write really small on the board, it's best to either sit really close to them or avoid taking the class with that professor altogether. See if any other professors are teaching the class at that time, or maybe wait a semester and see if he or she is still teaching the class, or any other professors begin teaching it.
If a professor in any way treats his or her students as if they are less than he or she is, that is absolutely a warning sign. Professors, and teachers of any level, truthfully, should be able to comprehend that their students do not have the level of knowledge that they have. The reason that they are in the class is to learn and obtain this knowledge. Professors should never belittle students or make them feel ashamed or disappointed if they are confused. It is their actual job to lessen this confusion and make going to class an enjoyable experience rather than a burdensome one. They should never act annoyed at students, or show displeasure in teaching or just being in the classroom. Professors should be open to their students, and encourage them to ask questions when material isn't clear.
The mark of a truly great professor is when you want to seek them out, when you want to know more because they just make the topic so interesting to learn about. Students shouldn't be afraid to ask questions or approach a professor out of the fear that they might leave the interaction feeling more confused and ashamed than before it occurred.
It is not neccesarily a professor's job to make material "easier" by any means, but it should be implied that he or she provides a safe and welcoming classroom environment. With the right professor, student will go to class because they want to, not just because they have to.
If a professor is not exactly an "A", and there is no way to avoid taking a class with them, you are just going to have to do the best you can with what you have to work with. Reading the assigned textbook for a class can sometimes really help clarify material that was gone over in class. Usually, there are Teaching Assistants that are assigned to each class, and meeting with them might also be able to help give you a better understand of what you learn. You might also be able to reach out to other students that have been in the class, with the current professor or a different one, and see if they have any pointers or hints to help you retain more information.
Most of the time, the work and effort that is put in outside of class will make the biggest difference, regardless of the professor. You just have to be willing to try.