Here is a good article on mix building and EQ by John Mills, a live sound expert who runs the mix for guitarist/worship leader Lincoln Brewster, on his blog, TechTraining101.com. If you haven't already, I would suggest creating a log-in and password if necessary to access these articles for free.

He stresses cutting as opposed to boosting frequencies in the EQ because, to put it in layman's terms, it sounds better.