Help with facial expression drawing

We all know how to practice gesture and figure drawing... but how about facial expressions? is there any similar way to do a quick draw and just capture the essence of the expression?

Thanks!

Here's a tutorial by one of my favorite artists: http://tracyjb.deviantart.com/art/Lackadaisy-Expressions-193978013
Then, in those manga tutorial books they always tell us to start with simple comical faces on round balls serving as heads, which is pretty useful for really fast sketches : )