this is called 'mastering'.
it's best to let someone else that has those skills, apply the finishing touches to your best final mixes.
it takes years to get good at this.
years.
i've been doing it for almost 11 years now, and i still suck.
point is, if you want to do it yourself,
start by study.
here's as good a place to start as any in existence:
Mastering Audio: The Art and the Science https://www.amazon.com/Mastering-Audio-Science-Bob-Katz/dp/0240808371 another must-study:
The Mastering Engineer's Handbook: The Audio Mastering Handbook https://www.amazon.com/Mastering-Engineers-Handbook-Audio/dp/1598634496 after you get the basics down,
you MUST get your monitors and room up to snuff,
otherwise,
you're just guessing at how your mixes will translate.
so many decisions can be SUBJECTIVE, but too much hi, or low, or harsh middle, and any other spectral imbalance,
is NOT a subjective choice, it is a mistake.
but be aware,
there is a push to get rid of the typical 'hit the ceiling with level' of modern mastering,
and a lot of 'players' have automatically-leveling functions built into them,
but when you are talking about the 'art' of completing a finished album of songs,
and how they all work together,
that's called 'mastering'.