Before I start, lemme say that I assume everyone uses Audacity when mixing, because it's what I use orz. Totally correct me if I'm wrong!
It doesn't sound too bad, but dat volume issue. Did you compress the vocals before mixing it with the karaoke? You should also compress it again after you mix the vocals with the karaoke.
Definite EQ usage. Assuming you use Audacity, it sounds like you used the Treble Boost default setting...even if you didn't/have no idea what I'm talking about, you must must MUST compress after using EQs. They tend to cause volume imbalances. Mimi's got these strong consonants, & most EQs will emphasize them, so be careful. Also, I notice there isn't a smooth transition between the verse into the pre-chorus, which could probably be fixed with compressing. (Please notice how I'm stressing the compression here orz).
This song was a pain to mix though D: so don't feel too bad. I had such a hard time getting it just right OTL & I still think the mixing on it sucks. Don't get too discouraged!