I am a big fan of teachers who regularly ask students for feedback. This can be for a specific lesson, the class in general, or to gather suggestions for future planning. However, some teachers find it difficult to hold such conversation openly in class.
Another method I have used, that works very well, is to add a section at the end of a test, quiz, or exam that specifically asks for student feedback. I even give students a few extra points for offering the feedback as a "thank you."
This design doesn't (and shouldn't) take on some extensive/complicated format. As with most things, simple is best.
Ask two questions.
1. List three things you do NOT want to see changed about this class (or lesson, test, etc.).
2. List three suggestions you would like me to consider for future planning.
That is it. Two easy questions. Six pieces of valuable feedback per student.
Try it out and let me know how it worked for you.