What technique, plug-in, fixed mistake, etc. MOST helped your mixes?

In the beginning it was modest room treatment, ARC and a sub.
 
Then it was simply listening carefully to what I heard in the speakers, cans (4 different types) and the car.
 
Lastly, being open to what others hear. There are some members here whom I trust to listen to pre-releases; even if I do not always take their input 100% to heart their input is IMPORTANT to me. And, whatever else I may get from posting in the songs forum.

The track Mute button.
 
Both a joke, and a serious point..

Analog front end.  It really makes a difference for me.
 
The other thing is learning to listen.  It really does take time, but once you reach a certain stage suddenly tracking (and mixing) start to make sense and you can learn to apply the right tools rather than just twisting knobs and hoping for the best.

as for plugins, geist has been a lifesaver. If i want to create, say for instance, a bass loop, i can grab my bass, lay down a line  using threshold mode and in under a minute i have a loop recorded, sliced and mapped across pads.

dubdiscipleIf you have two elements that sound perfect in a vacum on their own and they share a lot of the same frequencies, odds are good they are going to ruin each other in a full mix.

I'd say that was a major breakthrough point for me as well, though I first realised it in a live sound context, long before I had a DAW (actually maybe 10 years before DAWs even existed). It can be difficult to sell that to some musicians though, so sometimes you need one mix for them to hear their instrument solo'd and another one for when it's in a band context. >:-)

There's so many "eureka" moments really, lots of little ones that sometimes come together to make a bigger one...

Realising that guitar tone and volume controls go down as well as up, and that the volume control can do much more than just make things louder or quieter.

How compression works, what it's for, why it's used and when it shouldn't be used.

What you'll get away with in a live performance you won't get away with on a recording that has to stand up to many repeat listenings in a completely different atmosphere.

Sound engineering and musicianing are not the same thing and require different thought processes, even though the jobs overlap.

The recording technology, whether tape and hardware or DAW, is a musical instrument in itself.

Finally, perfecting a recording is a task that is never finished, but at some point you just have to draw a line under it and say "that'll do, release the thing".

This is going to sound snarky, but I mean it: crtrl-X and the mute button. The more I remove, the better it sounds. Most of the songs on my YouTube channel are 8-12 tracks, but sound bigger than that because there's no competition for them. Also, I do imaging "in reverse." A lot of people start off with mono tracks and the mix becomes stereo; I start with stereo tracks panned mono, and the mix becomes more mono but with width. I always try to make the music sound like it could be live performance, and for that, it can't be too "stereo."
 
But of course, that's personal preference and has nothing to do with general guidelines, expect possibly for the ctrl-X aspect.
 
I'd also add this is a GREAT topic for a thread. 

Wow...these responses have already gotten me more in trouble with my wife...lol
 
One thing I've been doing a lot lately is trying to reverse engineer commercial mixes to see what's going on under the hood...not necessarily from a composition perspective, but mostly from a nuts and bolts EQ and panning perspective.  One of my biggest shocks (which seemed to contradict one of the responses from my mid/side thread earlier) was how much low LOW end is contained in the side channels.  And this simply isn't a case of my mixes "not having enough bass", because (as I've discovered), raising the level of the bass/kick does absolutely nothing for the side channels.  Thank you Ozone and ears for helping me figure that out.  Latest releases by Keith Urban, Sara Bareilles, Nick Jonas (don't judge...lol) and country newcomer Sam Hunt have confirmed that.
 
So...one of my major advances lately in certain buses and even in the "fake-mastering" stage is for me to raise the bottom end significantly in the side channels.  It seemed counter-intuitive before...I even had Ozone stereo imaging bringing the sub-100hz info 100% to center.  Whoops.  The only thing I record outside the box is acoustics, so I boost the low end of those a lot in addition to the ITB electric guitar sims that don't benefit from any amp micing and corresponding low rumble.
 
Sorry to ramble but I'm a total mix nerd which is why I'm home on a Saturday... =(

mudgel
Mixing with my ears not my eyes.

The move from analog to digital concentrates our field of view with so many displays, lights, curves knobs sliders etc the tendency can be to use our eyes instead of ears.

If it sounds good it is.

+1 on that. I switched to using SSL 4000 channels on my mixes, no eq curve display, no spectrum analyzer, it's like mixing on a real desk. Just that small change made a big difference.

I don't just record myself. I got into taping b/c I love to listen.
 
Being mobile is really important to me. I love recording away from home or inviting new groups over to record.
 
Provides lots of good feedback from people who care (the band) and lots of opportunity to practice with different genres.
 
 

sharke
 
When you have complete control of the velocity/volume of each note, as well as all of the envelope/tone controls on the synth, there is often no need whatsoever for compression. 

This I completely agree with.
Guitar, Vocals, Bass usually get some compression in my mixes. I think it makes it sound better. Drums are more questionable - sometimes yes, sometimes no.

That when moving a fader up does not mean turning up the volume, but rather reducing the loss of the fader.

This might sound silly, but simple mic placement has been getting lots of play with me lately. The amount of mileage I've been getting out of putting on headphones, monitoring input, and moving a mic in front of a guitar cab is amazing. I recently tracked clean e-git for a raggae act and had to do no eq at all...just an 80ish low cut and that was it. If you're just slapping a 57 on-axis an inch out from the cab you're really missing out. And it's not big moves...small moves make big changes, especially with axis. Want to cut the HF harshness from a 57? Rotate the axis a bit. Also, rotate your vocal mic a few degrees off axis to save yourself a bunch of de-essing.
 
Save processor cycles...use less EQ and just move the mic.
 
Dean

ce
cut instead of boost

yes mister!