I just wanna say a thing or two about one of the most insanely simple concepts I've learned from the amazing Scott Kieklak. The freakin mono button: Use it! I've been doing mixing for hire for about a year, and you have no idea how much my mixes improved once I got Scott's advice.
I've told people about this before, and they usually just say I'm retarded and argue that "it screws up your stereo image and has nothing to do with how it's gonna be heard and blah blahblahbkdsnsl." Well, all of those people are dumb. Just try it. It's the truth. Unless someone is listening to music with headphones, it isn't going to be very stereo.
If they listen to it through a laptop, a small boom-box (shut up, it's not a lame word), or those little speakers that you plug iPods into, it's gonna be pretty mono. Think about it. Those speakers are uber close together, and most of the time, it's playing from across the room, so there's no stereo information left by the time it reaches you. Not only that, but a lot of radio stations broadcast in mono.
I'm not saying that you should mix your stuff in mono. Just check it in mono. If there are phase issues, you may not hear them until it's in mono. If you pop it into mono and suddenly all your low end drops out, then you have a problem. When you use those stereo synth patches that are all crazy sounding and flippin from hard left to hard right, you need to check that crap too. I've mixed some dude's some and it had a synth like that, but in mono, you could barely hear it. I could only notice it in stereo because it was obviously jumping around, but to a person who has it playing across the room on small speakers, that synth isn't moving.
ALSO, if make something pseudo-stereo by making a fake copy of an instrument by using a super fast stereo delay, it's gonna sound crappy and phasey in mono, so you'd better check it and do what you can to fix it. Even if you make a copy of something in Melodyne, alter it pretty good, then throw it in the opposite speaker, it may end up sounding phasey.
I could ramble on about that for a good while. I just thought about it while I was mixing something just now. I've been doing it for months ever since Scott told me about it, but I just now remembered how big of a difference it makes.
TL;DR - Mix in stereo. Pan all your crap how you want it. Check it in mono. Adjust levels, EQ, or whatever.
NOTE: If you try this with Logic 9, it may not work. The mono button on the Stereo Out doesn't work properly in some copies (if not all) of Logic 9. Just route everything to an aux, then to your Stereo Out. Use the mono button on the aux. In Pro Tools, some plug-ins let you switch the signal to mono, so you could put that on the master fader, but I just send everything a stereo aux first. Then you can just switch the panning between <100|100> and <0|0>. Plus, plug-ins on the master fader in PT are post-fader, so I use an aux first anyways just so I can use pre-fader inserts on my whole mix.
Ok, I'm going to bed. I feel ridiculous for making a blog post about the mono button, but it's a big deal, people.