Assuming that the mix is in good shape, that every instrument sounds as I want it to and is placed where I want it to be placed, I'd touch it up with one of the mastering EQ's at my disposal.
I got a license for Eventide/Newfangled EQuivocate when it first came out, and I also have Soundspot Overtone and Samsara Passive Stereo EQ (which is a Manley Massive Passive workalike). I recently got iZotope Ozone Elements 8 and have been messing about with the EQ in that suite as well.
When I get better versed in the ways of the wily multi-band compressor, one of those might make its way into my master FX chain.
Along the way, of course, it's important to reference the master against existing songs that I think sound great and well-balanced. I can also get a visual representation using Meldaproduction's MAnalyzer.
So what do you do?
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