Mastering music is by far the most complex and misunderstood aspect in music production. I lot will struggle and it takes a lifetime to learn. Don't get frustrated mastering a track, you aren't meant to.
Mastering was a big deal back in the day because tracks needed to fit and sound nice on acetate/vinyl. It also needed to be as loud as other tracks and there was to be as little stereo phasing as it could make the needle jump.
In recent years, with the advent of CDs and digital djing strict preparation of tracks for vinyl was a bit relaxed. Most tracks these days get a compressor thrown on the master bus and it's off to beatport.
Now keep in mind this is all my opinion and it may be warped to some people. A few engineers my facepalm and think I'm an idiot. It's all the same.
Mastering is no longer important.
Now hold on, don't stop reading. Mastering to me is making sure the track is not clipping, is as "loud" as other tracks, has a small bit of reverb and stereo separation on the higher frequencies and making all the sound kinda "mold" and "squish" together.
Mastering is can not be a magic wand. A PSP Vintage Warmer preset will not make a poor sounding track into an ACDC record.
The key to good tracks is the mixdown, making sure everything sits well together at a lower volume making sure to not clip then compressing/maximizing the master bus. Processing the sounds with eq, compression, limiting and sidechaining. You should never try to boost the bass on the master bus as it will effect the kick giving you mud most of the time, boosting the bass should be done on the individual bass channel unless you know what you are doing.
Plug ins are stupid, don't assume they know what you want to do, some are dynamic but hey don't have ears sitting next to you, give smart plug ins another 10 years. I used to stare at meters and analyzers all the time till I failed to see what hey were telling me, use your ears!
Also the samples the majority use are pre-processed. The Vengeance guys have there kicks and other sounds made to the same standard, volume and processing. Producing with these samples is adjusting volume, eqing and adding effects basically, you make all your sounds based off the other sounds to make everything in harmony, compressing the leads, pads and basses.
I don't buy into the whole "loudness war" hype, songs are louder that what they were 30 years ago and this war applies to commercial music, don't listen to all that noise people say. Dance music is supposed to be loud, compression can be used to extremes and sound good (listen to and Justice track). If it sounds good use it, as long as it doesn't clip and make ears bleed. You can still have dynamics and shake a club.
Best mastering plugins are as follows:
The waves L1, L2 and L3 maximizers are a bit of an industry standard. People love the L2 and hate the L3 and others dig L1 only. It's funny reading arguments about them, I think a blind listening test is In order comparing them.
PSP vintage warmer is a favorite of mine, it adds some analog fuzz and it just sounds unique. It has a nice limiter as well. I use it on all my tracks now. The great thing about it is it can add extreme drive if you wanted. An amazing algorithm under the hood I would imagine.
Izotope Ozone may be called ToysRUs by some but its a mastering suite that all who are new to mastering should use. It had a nice EQ and limiter/maximizer. The limiter is a simple slider that you can easily adjust make your tracks LOUD. I use it from time to time still, I now have the computer power to run it's EQ on individual channels, the EQ has analog and digital modes with extreme cut. Izotope released a stand alone EQ but it lacks what this has.
Long story short it's - make a great mixdown then master to make it sound a whole lot better. Don't try to polish poo.
Think of it like making a sculpture with a chisel then buffing it to make it shine, as a posed to using a buffer alone to make the sphinx.