A good mix starts with (not in any order)good musicians, good song, good engineering ,good room.
If you’ve got those then your mix will be easy. If it’s recorded well, with good musicians playing together in a good room then it will have a natural 3’D depth that’s hard to replicate when layering in a project studio.
Also good musicians self balance: I spent 20 years working with Mark Knopfler and his whole studio thing was; if things are working well then the faders should just be level on the mixing board, no or very little automation as it’s not needed when you’ve got great musicians/songs/arrangements.
All that said, musical genre’s vary greatly and if you’re into EDM for example then there’s no such thing as the band and therefore you’d have to take a different approach, and usually people who mix EDM generally aren’t mixing country records 
So my point:
Your mix starts the very beginning you start recording.
MC