What is the best way to solicit teaching feedback from students (before the class is over)?

I sent my students a feedback form (I'm a TA) and I got three responses. While they were helpful and informative responses, I am not sure how to interpret them, because there are only three of them and they all disagree with each other.

What is the best way to get feedback from students? Should I enter them in a drawing for a $10 Amazon gift card?