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.
Enjoy!
(Editor's note: the link in this article has since been updated, but the essence of it remains, hence its preservation here. The Google Now feature has since been discontinued, although the basic idea is arguably still intact in the form of Google Assistant.)