Abstain From Judging
As someone once advised, “Grow antennae, not horns.” If you prejudge someone as shallow, crazy, or ill informed, you automatically cease paying attention to what they say. So a basic rule of listening is to judge only after you have heard and evaluated what they say. Do not jump to conclusions based on how they look, or what you have heard about them, or whether they are nervous.
In fact, a good exercise would be to go out of your way to listen to a difficult speaker. Maybe he talks with a thick accent. Or talks much more rapidly, or more slowly, than you, or uses a lot of big words. Whatever difficulty this speaker poses, seize it as an opportunity not to prejudge but to practice your listening skills. Given some time, you will become more comfortable and effective in listening to diverse styles.
Stumble it!

