Maybe you have never tried Google Now (if so, start using it, now!) for anything. Maybe you're a Google Now power user. Either way I'm sure that you don't know everything that Google Now will do for you...until now.
The guys over at TrendBlog have compiled a great list of Google Now commands that will give you the ins and outs of what you should say to your phone. Just not in public, a lot. It looks weird.