You probably already know on some level that mixing is mostly a subtractive art form. And so any good mixer will be using cuts about 80% of the time and boosts roughly 20% of the time.
The rule of thumb I hope you’ll find useful is it’s much better to cut too much from everything and then be very selective about where you restore fullness, than to not cut enough and get a mediocre and mucky mix.
Once you’ve got a lot of open space to work with, it’s much easier to add frequencies back in, than it is to fit another person into a crowded bus so to speak.
There are 2 main techniques I rely on when I’m EQing my mix. As I’ve said before, I prefer to approach EQing in broad, even sloppy terms. It isn’t necessary to be misled and think there is only one right way to EQ something, there are typically a few, and it’s your job to find one quickly so that you can move on with it.
When I say quickly I mean that EQing is actually a messy and gradual process of refinement. That means it’s really about little by little, sculpting and shaping our music into something we’re gradually becoming more and more pleased with.
It’s really helpful to understand that you're only making decisions as quickly as you’re comfortable. And so make you're decision comfortably fast because sticking in one place for too long risks overanalysis.
Over-analysis inhibits creative decision making and worst of all leads to increasingly worse decisions. That is why while mixing I like to use a technique I call Slingshotting.