My goofy cryptic (but absolutely applicable) answer for the day - How to premaster mixes**
(1) Listen to the mix with blank objectivity.
(2) Realistically and purposefully visualize mentally what the mix's potential is - Mentally establishing what it "should" sound like when it's done.
(3) Set up and put in order a chain that will give you the reult you're looking for. Apply the settings in your head to the hardware (or software) chain.
(4) Listen to the result.
(5) Tweak.
** This is assuming that we're not referring to a "smash it into a limiter to make it loud" thing.
The most important step, and the reason that most M.E.'s will never master their own mixes, is step 1. You (and I) cannot listen to a mix that you're intimately familiar with at the track level with true objectivity. Attempting to do so is little more than second-guessing your own mixes - If there is something to be fixed during the mastering session, it would be FAR more efficient to simply go back and fix it in the mixing phase. And mastering mixes on the same system they were mixed on? (!?!) That's a completely different can of worms (for another thread at some point I'm sure).
Step 2 - Realistically establishing the potential. This is where there are no shortcuts - Experience plays the biggest role here. Listening carefully and imagining what can and connot be tweaked. What should be brought out, what should be pushed back. Mentally establish the energy and feel of the finished product without actually hearing it.
Step 3 - Setting up the chain - Again, after steps 1 & 2, this is where everything can go completely awry. To keep the objectivity, 90% of this should be done without even hearing the audio. It's not a time for experimentation. Anyone who has ever "mixed themselves into a hole" (I think everyone's hands are raised right now) can relate to what happens when you experiment on a project that you're working on - Which leads to a rule of training - If you don't know what your gear does, experiment on something that doesn't matter. The point is to instinctively know what will happen with this or that processor with this or that setting to this or that mix. Not to "perfection" - But you should be able to mentally establish what EQ tweaks will need to be made. You should establish what type of dynamics control is needed and the "rough" settings for these controls. This is NOT the time to "throw a maul-the-band compressor on" and "play" with it - That's the surest way to get yourself into that "hole" discussed earlier - Ears adjust quickly - You have to be one step ahead of them. Establishing your chain before hitting the PLAY button again allows you to immediately compare without prejudice, between processed and unprocessed material. Which is essentially step 4.
Step 5 - Now that your settings are right in the ballpark, it's a simple matter of tweaking it a bit. Maybe the release time on the compressor wasn't quite right. Perhaps you were off by a little on the frequency on the shaping EQ. Maybe the corrective EQ was too strong or not strong enough and it's playing with the compressor. Etc., etc., yada, yada...
And again, this whole theory is based upon two important factors - (A) The engineer can listen without prejudice and (B) The monitoring chain (including the room, of course) is superior to any previous chain in the process.
"Pro" mastering every time? If you can, sure. If not, the best thing you can do IMO, is use the "buddy" system. There are only about 3 gazillion home engineers out there. Network a little. Work on each other's projects. Critique each other's work. Learn YOUR skills on something that you haven't heard - It's the only way you won't be walking backwards in your own footprints.