Student feedback can be a very valuable instructional improvement tool.  Often student feedback is given at the end of the course in the form of a standardized evaluation.  There are a set of questions that cover the range from the classroom/lab environment to how the students perceive the instructor and his/her ability to communicate with students.  While these evaluations have some benefit they occur at the end of the course when nothing can be done to adjust the instruction during the current course.  Another way to use student feedback is to get input from students throughout the course. 

After an assignment, quiz or discussion session give students a 3X5 card.  Have them write down how effective they thought the assignement, activity, etc. was in relation to helping them learn the course content.  This exercise will only take a few minutes but the payoff will be well worth the time.  You will find that the students will give input that is accurate and helpful.  You then can take this feedback and make any changes you feel are appropriate as you make the next assignment.  This way you are customizing your instruction based upon the feedback that is given.  So the current group of students benefits from the adjustments rather than the next class of students that take the course.  You will find that the end of the course formal evaluations will be be different as a result of using the ongoing mini-feedback format.  The students will see you as an educator that is listening to them and making adjustments that will help them to learn the content and make progress toward their career goals.