What headphones do you have?
Fundamentally, I would strongly suggest to work towards the following results, in no particular order, and in the long-term sense:
- Go for clean low-mids, i.e. lack of muddiness in the low-mids (~200Hz)
- Go for crispness above 10000 Hz (not-dull treble)
- A midrange with room for instruments to breathe, but not so little midrange overall that it sounds "hollow" (500~4000 Hz)
- No overcompression (this is hard unless you have a tolerant limiter or you want to mix quietly)
- What leads should be audible enough but should not overpower background instruments; try adjusting volume from below the expected final result, instead of from above. I detected volume changes more easily back then when I started below the expected perfect volume.
- Percussion and drums should be audible the whole time but not too loud, i.e. don't let them get buried, and don't let them smash the limiter and create overcompression, pumping the whole mix down, and don't let them smash a soft clipper and clip the output.
And one overarching goal:
- I think about this constantly. If someone else has all the resources that you have and all the skills they will ever need (in other words they're exceptional enough), can they listen to your remix or song and recompose what you have written by ear from scratch (within reason)? If they're going to have trouble with that, then there's something off with the mix. Once you consider that, you could then imagine what you would have to do to make it so it would be more possible for them to do so, and give that a shot. At some point you might say, "eh, it's good enough", but if you're uncomfortable mixing in the first place, I think you should just keep practicing until you can confidently say "eh, it's good enough now. Any further is just super nitpicking".
What I think you shouldn't do is try to compare songs of completely different genres. So don't compare metal with orchestral when it comes to mixing because they appear to be completely different when you disregard the objective mixing aspects. Metal to metal, definitely though. Basically, the above points apply for practically everything in some sense.