Since every production is unique and since your goals are relating to the production, your goals are to some extent automatically also unique. And the frequencies when they combine as dry tracks are also unique, therefore you have a lot of content dependencies when you start mixing. I find it's not optimal to lock down your creativity by trying to fit the content inside of the same specific parameters.
But some ballpark figures for me when I mix a pop or country song is I want the fundamental somewhere in the range 1,5 kHz to 2,5 kHz at -8 integrated LUFS when it is a female singer, which basically indicates that the height of the mix is pretty good and there is not low end energy present that is eating up the mix. If it sits somewhere in that range I know that it might be a mix that is now ready for mastering. During mastering I will then tune the loudness +- 2 dB depending on where I find its sweet spot is. In a loud EDM track, where you need quite a lot of low end attack and mid frequency intensity on the kick drum, then the low end will typically average somewhere around -22 integrated LUFS, cumulatively louder towards the sub frequencies within that average.
But, specifically, how do I know I have the low end at a good level from project to project? Well, basically I don't, I just dial in a balance that I think listeners will appreciate. Having said that, I do have specific monitoring when dialing in the low end in order to get the right attack characteristics and I do have specific monitoring for finding out do I have too much or too little low end. This is very important in mixing and mastering to be aware of. The meters are mostly just rough confirmation points, but can be of great guidance when the ears start to get tired. I do try to get the mixing and mastering of a song into 4 separate sessions, each session with specific goals. And I very often compare the height of my master against reference masters I like. On top of this I always print a number of masters of the mixes with various candidate dynamic profiles, the low end will often vary a little. Finally my ears (mostly) and my thoughts decide which print I like the most and it is the low end level of that version that automatically becomes the final. Sometimes a bit dark, sometimes not, it all depends on how it sounds, feels and progresses. A mix that is too low end intensive will not generate a lot of listens over time, so when I evaluate my prints I try to observe it objectively from different perspectives, these perspectives are technical, musical etc.
When you dial in the low end, pay attention to how that impacts on the rest of the frequency range. You can also set the vocals quiet in the mix to see is the low end then completely taking over, because if it does it struggles for room inside of the mix, you get a dense low end in that way. During mixing I tend to leave the bass guitar muted far into the mixing process, because the bass guitar can be very distracting and very sound enhancening, the combination might not make you work on the other sound sources the way you need to. Similarly, if I have some great sounding sound sources in the mix, I mute those because I know they will end up great anyway, typically some soft sounding electric guitars, those I instantly mute and my focus might then directly go to the piano that might be a bit edgy in the mix. I try to isolate that which is important and needs work inside of the mix, so that when that sounds a lot better I am now ready to bring in the sound sources I know will further enhance the sound of the mix because of how great sounding they are. So I basically try to remove all of the "glitter" about the mix, so that I can work on its raw strengths and weaknesses. This I also do during the mixing readiness evaluation stage, because often it's better to improve the production/arrangement/recording. That's often the case if the fundamental sound sources like kick, bass, snare, vocals are not good sounding, they must be good enough sounding when you start mixing. But when I mute great sounding elements, I don't rely on those making everything great at the end, my absolute goal is really to make what I have left stand on its own feet (express a great sounding mix on its own). This work can be quite heavy at times, but with Ian Shepherd's perception plugin I know that I am bit by bit making it better sounding, so that kind of directs my work towards a constant audio improvement towards my end goals. But those end goals I set especially high compared to the rest (which is why most of the hard work ends up here), because I know they will be having a somewhat dense impact on the mix compared to the rest of the elements in the mix, especially if its the vocals or snare. A great sounding mix is produced and recorded well, but also improved well during mixing and mastering.
