I was sitting at the mix at work last week and thinking about how I could make my reverbs sound better. I'm a little strapped for I/O right now due to feeding a lot of monitors so I'm actually using a group to send to my vocal reverb. If it was on an aux out, my Midas has some EQ built in, but as it is I'm stuck right back where I would be on most any other console.
I kind of gave away the idea there. Reverbs can only do so much, even really good ones. So it's natural to look at one and start to EQ the sound coming out of it. But what about the sound going into it? If you find that a verb is boomy or nasally, or maybe a little too sibilant, it's only natural to grab the channel EQ when it comes back into the board and start to tweak. I find that you can generally make some improvement, especially if you're in a hurry, but there is a better way.
With the advent of affordable multi-effect processors like the M-Ones I have at work, you can just add an EQ in the signal chain before the reverb. Many have a high and low pass built right in to the verb section itself while others will let you add a graph or parametric. Then there's always the tried and true method of patching in an actual EQ. I've got an old Ashly seven band parametric kicking around the bone yard that I've been pondering for the purpose if I can't get what I want out of the built in EQ.
All this applies to mixing in the box as well of course. If you're new to the idea you may want to try it out in a DAW before you invest in more equipment for a live rig. Being able to see the curve on the screen can be a big help when learning what sounds best. There are some general rules you can follow, that is of course until you decide to break them as it suits you.
For beginners, treat a vocal reverb EQ like you would a vocal channel, trimming up the lows and touching the mids a little, and take some off the top if it's too "ess-y". For instruments just play with a band pass or pair up a low and high pass to make your own. Tune to taste. Myself, I like to tighten things way up for drums, but not always. Use your ears.