hey, everyone. I'm just gonna share something that works for me on the electronic production side of things, and I want you opinions and feedback.
Basically, when i'm mastering, I drop a, Eq post-compressor, lift the highs a little for some added crispness, *maybe* boost the low end, and finally, I generally end up pulling 80Hz down about 6dB or so. This tends to just clean up my low end a bit when it feels sort of muddy.
Is this a standard practice? Tell me what you guys are thinking.

No it is not standard practice at all. 80Hz is pretty low and if I was to start pulling out energy around that frequency the whole bottom end of my mix would change  (for the worse)
 
You need to work towards having a perfectly normal bottom end around 80 Hz at the end of a final mix that needs no attention. Maybe your monitors are letting you down here and acoustics.
 
What does tend to get clogged up a bit is that tricky area from 200 to 300 Hz and it is here I might put a slight dip in the response in mastering. That seems to clear the cludge away and the rest of the mix will sound better as a result too.

I often take out a bit below 80Khz on some instruments that have little need of it when mixing, like guitars or piano. But I think the bass and drums would suffer if I lost that much in the final mastering eq.

I'm thinking this is a case where I need to go into individual tracks and find out what is really being muddy. I tend to high pass a lot of my recorded tracks by default, maybe its in the soft synths... Usually my bass and kick don't suffer much when it's electronic genres- I put a REALLY hard spike at like 40-60Hz to get a really heavy thump. 
I think I need to generally change my workflow

dav,
needing to take that much at, at THAT freq, means you have buildup on your tracks during mixdown, at that area.
 
that IS common, it is easy to build up low end...
 
in fact, if you have just a heavy low end bass track, that alone can swamp your low end.
 
part of learning to mix well, is learning where to HPF, low shelf, selectively EQ, 
WITHOUT NEUTERING your low end.
 
the more you do it, the better you will get.
 
 
i found that it helps to use a visual aid at first (i use Waves PAZ Analyzer, but SPAN works just as well, and is free)
 
you study every track, and get to know what is happening in the low end, and train your ears to hear what it is that your eyes are telling you is happening, until you get to the point where you do not need to see it anymore.
 
part of it is intellectual, but part of it is learning your mix enviroment (your room, your monitors, etc)
 
the idea ultimately, is to be able to bring your faders up without even touching EQ!!
 
LOL, that is mostly pie in the sky, but in a perfect world, you would have each and every track sounding exactly the way it needs to sound for the mix, going in.....
and additive eq would not be necessary.
 
 
of course, to pull that off, requires a lot of nice expensive mics, preamps, outboard compressors and eq's, etc...
but you can use a minimum of equipment and get very close to that 'ideal' situation by studying what you have, and what happens with it, and learning how to work around it
(if your mic has a built in peak somewhere,  maybe that high end harshness you hear sometimes, is just a collective build up of that particular frequency from the mic on multiple tracks......... that kind of thing.)
 
 
if you do freq analysis of your favorite pro tracks, you will probably see some serious carving out of the low end, and what is left, is to help make bass tracks and kick drum tracks really stand out for crappy little speakers...
 
 
for example:
brand new tune, by Queens of the Stone Age, "My God is the Sun"
 

 
notice the huge dip at 150...
but the large peak at 100...
and notice how it totally falls off from 100hz down....
 
not a lot of 80, or 60, or 50, but it lifts back at 40hz....
 
 
there's a reason, if you listen to the song, it may inform you more.
 

also, look at the boost at 200.
 
why?
 
big dip at 300hz, why?
 
big dip at 3khz...
 
etc.

I agree with batsbrew about the very low end. Having done quite a bit of mastering on pop music especially what I found was not so much what was happening around 80Hz but the slope of the roll off below about 50 Hz. The roll off can be quite steep in a way but you can still maintain a nice punchy low end even with a little deepness in there too.
 
My car stereo really sorted this out for me. I have got a killer sytem in the car but the low end is quite deep and powerful.  (over the top a bit actually)  What I found was most commercial releases had a nice punchy low end without too much deep notes in there but still just enough.  At first my mastering was rattling my teeth in the car so I realised something was going on.  After doing what batsbrew did with looking at the EQ curves of a whole range of commercial releases I found they all had a very common low end slope.
 
All I had to was to recreate it and before long I was getting exactly the same low end sound in my car as the commercial releases.
 
If you are getting build up around 80Hz then it means there is a build up from individual tracks and they need to be investigated a little more rather than attacking the final mix.
 
It is good to talk about the low end though because this is where MANY go wrong in that they get it screwed up. I have found over the years you need less low end than you think. (especially the bass) It is a matter of getting it in proportion to everything else. Not overpowering everything else.

Dave, the cleanup you're experiencing is from removing low frequencies that don't contribute much musically but that have a big impact on your bus compressor and limiter. It's most obvious on genres that shoot for high loudness, where it can be counter-intuitive that reducing low frequencies can actually increase bass perception.
 
One of the main genre differentiators is the frequency of the highest level in the spectral graph. As bat illustrated above, that frequency is often a lot higher than you might think, often around 100 Hz and as high as 170 Hz. The exception is music meant to be played on large systems at dance clubs, because the producers can assume that there'll be some benefit to including a lot of < 100 Hz energy. 
 
But for most genres, energy in the very low frequencies is wasted on 99% of listeners. And not just those who listen on stock earbuds with a serviceable low end of maybe 150 Hz, but also those who listen on car stereos and boomboxes and modest hi-fi equipment. 
 

This about explains it. Now all you have to do is put it into practice, and make it sound like you want it to sound.
http://www.audio-issues.com/music-mixing/all-the-eq-information-youll-ever-need/
 
But there are curves to your ear also. Sensitive usually at 3.15kHz (3150 Hz) and midrange-y at 1000 - 2000 Hz (1kHz-2kHz).
Down those somewhat ( couple of decibels).
 
Liveness of sound - 4000 Hz (4kHz) like a live band perhaps.
 
The rest of what the second chart shows - fullness of bass or sound - 100-200 Hz or 200 - 400 Hz like the second chart shows.
 
Then you adjust for the hearing of the ear, which is another chart or Fletcher-Munson Hearing Curve at what loudness level (which is how you hear it).
 
http://sessionville.com/articles/what-is-the-riaa-curve
for vinyl records (or the old phonograph recording with vinyl and needle)
old yes, perhaps you never heard it.
 
The first link is about it for digital and CD making (DVD), but perhaps it does not hurt to know such info.