I personally mix as I go, so I usually have a progress mix version and a detached mix version to compare. So before I get ready to mix the track, I'll version it out as Project_ProgressMix and Project_PreMix, then just version out the premix to Mix_1/2/3 as needed and use those to prevent messing with the earlier project files.
The way I was taught (which isn't necessarily the best) was to disable all non-sound design mixing effects, reset all pan pots and pull all faders to -Inf dB. Start ranking your sounds by importance, and bring up their volume to a clearly audible level one by one until it's all forming a nice gel based on levels alone. Then you repeat the process with pan pots, then with EQ to whatever needs it, then with compression to whatever needs it, and only then do I start worrying about creating the physical space all the instruments are in with stereo imaging and delay and reverb and all that fun stuff.
Since I didn't delete the old effects and just bypassed them I can test to see if my new attempt was better or worse than the old one, and if I wanna see if my level balance is better I can just A/B the two projects.