i don't think you can ever stop learning about mastering. I'm no well, uh, "master" but I'll drop a technique Steezo told me about a few years ago. This was when I had no monitors but only headphone monitor joints. Use whatever plugin/software ya usin and always do it at a low volume (kind of like mixing) get it to were you think it sounds nice, get up and walk away. I have to. Give ya ears some rest. Have a smoke or sumthin and come back. Listen again. If you are happy, save it as "Name-Master" and get back to it. I really think takin small breaks inbetween mixin/masterin is good. Once you come back, listen on the monitors or headphone jammys, and then get a good set of stereo monitors and listen thru there. Go between the two and just explore. I'm not a technical dude, but I think this could work for anybody.