How do you make your students smile?

I was reading an article from the We are Teachers blog about ways to make your students smile.  As my students were packing up, I was discussing whether these 10 things would work for them or not and what inspires them to be motivated.  One of my students said I motivated them because I always smiled at least once in class. That they could tell I enjoyed what I taught and I was excited about it and positive.  They mentioned some teachers they've had in the past complain about their duties or just lectured as the students took notes without even smiling.  They want to try harder in my class because they know I enjoy being there with them and sharing my knowledge and interests.
Who knew a smile could go so far?
That made my day, especially, since this past week I've felt as I haven't been the "bubbly encourager" my students view me as.
So from now on, no matter how many extra duties or last minute meeting are thrown on me I'm going to constantly remind myself- it's not my students fault.

How do you make your students smile?  How do they perceive you?