I paid for a couple of my projects to be professionally mastered (not on Newgrounds), so I could hear how the professionals do it. Though, to save time, I'm trying to learn how to do it myself. I can tell that the mixing, which I did, was not up to par. So no matter how good the mastering, the mix must be good too. Though, the more I improved at mixing, the louder and better the mastering engineer's could achieve my tracks.
I'm constantly trying out new things and improving, but I'll share what I have discovered gives the best results:
1. I use a compressor to glue it all together. The compressor I use is The Glue (THANK YOU TO THE GUY WHO POSTED THIS - THIS COMPRESSOR IS THE BOMB!)
2. I put FabFilter Pro-L (limiter) on. I put this on the last part of the effects chain, and I apply a likeable loudness BEFORE I do the next steps.
3. I put in iZotope Ozone 5 in the effects chain between the compressor and the limiter. I use mid/side EQ to clean up the low end a bit, and maybe cut a bit of brightness, but apart from that, I don't use the EQ much. I try to get my EQ right in the mixing process.
4. I use the multiband dynamics to give some extra punch to the low end. To do this, I extend the low end band to about 150-250 (whatever sounds good), I set the threshold to around -1.9. Add about 1.9 gain, put the ratio up to around 2:1. Change attack and release to whatever fits the track (usually both 150-250ms). The rest of the bands I leave alone.
5. I may use some stereo imaging - mainly to narrow the low end a bit.
6. I use the harmonic exciter, most usually tape (and with oversampling). Not too much though.
I tend to concentrate on getting the mix right when working on serious projects. A common mistake is to rely on the mastering to fix everything.