The best candidate for mastering your tracks is a mastering engineer, there’s no doubt about it. But hell, even they once had to learn how it’s done.
So yeah, like most other self-taught producers, I like to experiment with mastering my own tracks. They’ll probably never sound like professionally mastered ones, but there’s no harm in practicing different mastering techniques.
Mid/Side equalization is one of those techniques and if you’ve never tried it before, this video tutorial may inspire you to do so. It was made in Ableton Live, but the basic principles can be applied to any other DAW. Btw, you can find lots of other great Ableton Live tutorials if you visit The Ableton Cookbook.