Reputedly the hardest part of the mixdown! Let's see what people have to say about this!
To me a track is flat without a nice, heavy bottom end! I pretty much appreciate most tunes that have power in this area.
My bass is usually made up of a few layers, and where the top layers are fairly easy to balance, it is the sub that is hardest to place.
I tend to EQ a hole for the kick, then low pass the whole track and play with the levels until they seem good. Then I'll AB the test with a similar finished track. I then repeat steps 1 and 2 till I am happy. Note: I always finish the drums first!
I wish it were easier!