From my experience and what I have seen from teachers, one simple way is asking students questions during and after the lesson. This helps us know what they understand and what they find difficult. Another way is giving students a small paper to write how they feel about their learning. Some students may be shy to speak, but they can express their ideas by writing.
I can also create a safe and friendly environment so students feel comfortable to share their thoughts. In this way, I can learn more about my students and improve my teaching.