And put the project aside for a day. When you come back to it, do the levels still seem correct?
Usually, once I get them settled, they are good.
When I introduce a new song, I balance them by ear in my home studio, and that usually works. But on the job, on a different day, things can be different. I also like to adjust the volume the day after I finish mixing the song. 'Untired ears' help that a lot.
Usually one volume adjustment, say cut the mixed audio by .5db or raise it 1db or whatever, does the trick. Sometimes two. I think the most I had to tweak was 5 adjustments.
Creating a backing track for a new song might take a couple of long days. Re-tweeking volume takes a few minutes. It's no big deal.
Some songs come together quickly, others take time. I record the drums, bass, and many of the comp instruments in real time, especially if it is a song BiaB can't help me with. But, if I'm lucky, I'll get to play that song to an appreciative audience hundreds and hundreds of times. If it's as good as I can make it, I'm happy, and it's worth whatever time I have to put into it.
Insights and incites by Notes