Welcome to The Tricks of the Trade, where you'll find quick tips for just about everything. Nina will probably find this one either old hat or interesting:

When mixing a record, a band member will often insist that a track could be improved if you make their instrument or vocals louder relative to everyone else. To please this person while not screwing up the sound, twiddle some knobs and then turn up the overall volume. Since the person making the demand will be focusing on their own part, and their own part will now be louder (along with everything else), they will usually think you've fulfilled their request.

I guess you could also call it Headology 101.