Do some reading in advance to get familiar with the new vocabulary. I don't know enough vocabulary. Again, this is a matter of familiarity with the language. Read as much as you can. Keep a notebook of new terms.
Different lecturers have different pronunciation.
Yes, they do. Once you have decided that it is the lecturer's pronunciation, and not your lack of knowledge, that is creating a difficulty, you might be able to discover where he or she comes from and find out the characteristics of speech from that part of the world. You won't be able to change the way the lecturer speaks, but you might get to understand him or her better. Some lecturers use strange idioms. Yes, this can make it very difficult for non-native speakers to understand.