My question to you and others is: assuming I have done a decent job mixing, what are the things you would always include when you master a song? What are those "never forget to do" kinds of things that you might do on each project?
There's the rub -- There isn't anything specific other than bringing it to its final form before distribution (the true definition of "mastering" anyway). Other than that, it's 100% listening and letting what you hear guide what you do.
Doing that to your own mixes is exceptionally difficult in the first place (which is why you rarely find a mastering guy who will work on his own mixes or a mixing guy who will master his own mixes). When you listen to a mix you're intimately familiar with, you're hearing what's there (something you've heard a half-zillion times already) and your brain is likely filling in a few things also (the way your brain "wants to hear it" is how I usually put it). Any objectivity has left the building long ago.
When I listen to a track here for the first time, I listen to a chunk (5-10 seconds), another chunk, maybe one more chunk, then I shut it off. I set up the "obvious" stuff -- maybe it's 2dB heavy at 200, a few heavy at 400Hz on the side info, needs a cut at 2.5kHz in the mid info, a boost at 10k in the side info, x-amount of gain into whichever compressor it's craving, etc., etc., etc. -- Then I turn it back on and do my best to ignore it (this is where forums come in handy). I let it play "in the background" and see if anything grabs my attention -- Clicks, pops, hiss, video whine (it still happens), sibilance and the like. Trying to stay "detached" from it -- Once I start tapping my feet, my objectivity is waning.
THEN I actually give it a good listen -- Tweak the settings I already set up -- maybe I pushed it too hard, maybe not hard enough, maybe the extra push means another .5dB down on that 2.5kHz cut, maybe it's craving a little more "flavor" or shelving (the BAX is probably there already with high and low cuts, but this is where I'd start messing with the shelving adjustments).
But long story short, 90% of the settings are decided after the first 10-20 seconds. That last 10% are over the next several minutes. If it doesn't follow that sort of plan, there's some other sort of "surgery" necessary (okay, that's normally obvious from the first 10 second chunk).
That's the everyday --
Now on the rare occasion that I'm working on my own mixes (it's incredibly rare, but there are a couple artists I work for with some regularity who insist on it), it's as simple as throwing a limiter across the main buss and controlling the damage (for lack of a better term). If something stands out, I fix it. If it doesn't, I'm done. And I *still* insist on giving them a set without any limiting on the main buss in case they ever want to send it to someone else for mastering (and I usually suggest a few people while I'm at it).