Many live sound engineers sometime make life difficult for themselves by confusing when to use the various types of EQ. For instance, if you use your board EQ more for tuning the room, you'll find that it will take you longer to tune the system every night. Instead, the board EQ should be used for just EQing the mics to either the vocals or instruments onstage, while the system EQ is used to tune the room. That way, there's only one set of equalizers that change from venue to venue.
Here's an informative video from Dave Rat ofRat Soundthat explains his method (and that of most other live sound engineers) of EQing a live sound system.
One part of this that's a little different is that he uses a set of headphones that he knows well to EQ the stage mics and as a system reference. Make sure you really know your headphones well if you choose to use this trick.