Thanks, notbradsohner!
Seriously - If you've got great sounding mixes, the last thing you want to do is master them on the same gear using the same ears that mixed them.
I don't mix very often anymore, but one thing I almost never do is master my own mixes. I used to do it often. Then I got into mastering more seriously and realized VERY quickly that it's a bad idea. Mastering anything that you're really familiar with takes away your objectivity. You'll notice details you don't need to while ignoring others that require attention.
Mastering skill don't develop overnight - It's a fairly involved process. One thing I would HIGHLY recommend is getting your hands on music you've never heard before and taking a whack at THAT. This is the same reasoning with not mastering your own mixes. Even if it's just another engineer in the same position as yours, maybe do a little "trading" of mastering services for each other to help develop your technique.
On the question of "what to do" - That's going to change for every single mix you work on. You need to listen to the mix for only several seconds and "visualize" what the finished product should sound like. Then, shut it down, set up whatever you need to get the result you're after, get the controls where you think they should be as a good starting point, restart playback and tweak away.
