The excellant GoogleGuide (not affiliated with Google) has pulled together everything you need to know (in exhaustive detail) about using search queries effectively, whether you are a novice or advanced user.
If you're sporting Android 4.1 Jelly Bean then one of its most notable features just got better, as an update for the Google Search update is enhancing Google Now (still getting adjusted? check the guide book for a list of commands) functionality in a few key ways.