Here are some techniques and things I used improperly for a long time that I think will help you. Luckily for you, I've researched a lot of techniques for dubstep and EDM in general. And I have a lot of experience with NI Massive.
What I did for a long time was use the EQ too boost the loudness of my instruments which is NOT what you want to do. Using the EQ to effectively layer the sounds is key to removing mud from your track. Some people like to do this with multiband compressors but I find this to change the overall sound sometimes, and if overused, it can peak pretty bad.
One really good technique which most new artists under-use is using the EQ to have each separate sound fill out certain and varied frequency ranges to reduce overlap. For example, what I like to do is have my kick drum raised with the EQ at ~100hz and lowered a decent amount at ~200hz and lowered significantly around 30hz to 60hz. What this does is make room for the common strongest frequencies of the snare (200) and sub bass (30-70). For a more specific and personal touch, I sometimes raise the kick at an extremely high pitch frequency (varies on the song itself) which gives it that slight high pitched punch often used in EDM and lower then the mid ranges very slightly too to make room for my synths and to. Next, I do the same thing as earlier with the frequency specific EQing to the snare and sub but oppositely. Raise the snare ~200hz and lower everything below that a good amount. I like to cut off the really high frequencies on snares but that is just me. Then with the sub, I boost it at 30-70hz and lower everything from 120z and above. Significantly so on the higher frequencies. Also for almost every sound in my song that isn't a kick drum, snare, or sub, I lower the frequencies at ~200hz and ~120hz and below. What this does is remove the overlap from the different sounds giving more room for the bass, kick drum, and snare.
Another thing to take note of is the overall image of the song. Generally highs are set to be mostly stereo with limited mono. Then with lows, are generally mostly mono, with very limited stereo. This is a technique I discovered fairly recently which has helped immensely.
Another tool that is underused, misunderstood, or overlooked by beginners is compressing sounds with a wide gain range. I'd do some research into how a compressor works exactly and when to use it. But to put it simply a compressor controls the peak and range of an individual track's gain level. Think of it as squashing the gain to fit within a certain range.
Specifically with dubstep (brostep actually, but don't mind the name even though it was created as an insult) growls or wobbles, I do the same as above (lower at 100 and 200) but raise it in between 100 and 200 to give it a little punch and then raise it again in the mid tones from 250-500hz or above. I tend to have a separate synth designated as the sub for wobbles and growls so that a sub oscillator within those synths will not distort the others. With non dubstep songs, I try to keep the mid range sounds separate from the typical dubstep sound range by generally not increasing it between 100 and 200hz. This really depends on preference and the specific song. Heck, it could sound great even in a trance song which typically aren't known for having overly strong bass levels.
The mix-down styles will vary from genre to genre and will depend on what samples or recordings you are using. Always use a spectrum analyzer to check the peaks of each sound and to find where some unwanted frequencies are. That is a key element to all of my mixing. Using compressors correctly will generally fix the peaking problem a lot of beginners have when mixing. Just be careful not to overuse compressors. I know many people who advised me to compress every element of my songs just because they were told it was a good idea. They didn't even know why it was a good idea or why they did it.
There are also some techniques specifically used in NI Massive. One is to add a dimension expander effect to do exactly what the name implies. Adding some additional voices under the voicing tab is a good idea too if you want to add more fullness to the sound. On envelope 4 (the gain envelope) a lot of people raise the main level so that the volume stays consistent while the note is held since it set to lower automatically after the initial note is played. One thing Skrillex does a lot with some of his signature sounds is use a hardclipper filter to give them more bite and intensity. Formant oscillators and scream filters are also a commonly used elements in dubstep songs and I personally love them. Don't forget to try out different settings, modulation effects, wave tables position, and amp position for the oscillators too. Also try changing the wave forms, like the default spectrum to bend+, bend+/-, bend-, or formant like I just mentioned.
Another thing to keep in mind is that you don't want to stick with only one synthesizer. FM8 for example is another great NI synth which is actually more often used by Skrillex than massive. Even if you used the exact same filters, effects, and oscillators in Massive as you did in FM8, it would sound totally different. This is because FM8 is an FM synthesizer while Massive is an additive synthesizer. Personally I've been falling in love with FM8 and reFX Nexus 2 and have been using Massive less than I used to.
WOOPS SORRY FOR THE TL;DR BUT TRUST ME IT IS WORTH THE READ.