Many of my students tell me that they find it really difficult to follow their lectures. Some of them tell me that they think they can only understand 25% of what the lecturer is saying! Now that is a worry!
My advice to my students is to try and do something about it. The most important thing for students to understand is that when they listen to lectures they need to be ACTIVE and not PASSIVE. There are a number of things that students, especially international students, should be doing BEFORE, DURING and AFTER the lecture.
Before the lecture students need to prepare! If you just turn up to the lecture not knowing what the lecturer is going to talk about then you are not helping yourself. You need to find out as much as possible about the lecture as you can before you attend it. Are the powerpoint slides available to view beforehand? Do you know the vocabulary for the subject? Can you read the relevant parts of the textbook before the lecture?
During the lecture you need to be active! Sit at the front so you can hear properly and so you can pick up all the facial expressions and mumbles and off-hand comments from your lecturer. Use an audio recorder if you can. Try to judge what is important and what is not important. Note down things that you can't understand to ask the lecturer later.
After the lecture form a study group with your friends. Sit down together and swap notes. Talk about what you understood and what you didn't understand. Find time to ask the lecturer about things you are not sure about. Write up your notes in longer hand so that you can understand them later.
I would strongly recommend students to work through the Listening to Lectures part of that great resource Prepare for Success which you can find here.