Get a good stereo mix with contrasting sounds in the L&R channels+a lot of side info.
Than hard limit/clip the master and you'll get to see a diamond on your vectorscope.
You shouldn´t be aiming for perfect a diamond perse, just make sure it sounds good.

Spread them out over the sides so it's not that present in the mid, usually works for me. You could use any stereo widening technique as long as it sounds good.

Don't know if you're having Ozone. But you could use the hamonic exciter in there to give the highs some more prescence (it gives the high end some kind of subtle distortion). After that you could widen the highs to the sides to give them more space. It also helps to treat the high end with the same caution as you would mix the low end (make sure freq's are not overlapping each other etc.). When I mix down my tracks I always want the click of my kick to stand out, so I try to mix the rest of the high frequency material around the click of the kick so to speak. Another issue that could be dulling the high end is an incorrect frequency balance of your mix which can change your highs massively when limiting or compressing the total mix. Check out the spectrum of a track where you like the high end and compare it to your mix. Hope this helps!

I think It's mostly about choosing the right sounds as well. While producing add a perceived loudness meter on your master channel (Like T-racks, Voxengo Span, FL Wave Candy in Leq(a) mode) and see what a sound does. A sound or song without any mid and/or high frequency content will never sound really loud. Subtle distortion on sounds can really add some perceived loudness (especially when it's adding harmonics in this range). When you've found the right sounds then you can squeeze some little more loudness out of your track in the mixing and mastering stage which is like Miles Dominic already said all about controlling and lowering peaks in the mixing stage.

Things I tend to do a lot:
- Serial compression in the mix and on the master.
- Harmonic EQ and distortion
- Multiband compression in the mix and on the master.
- Controlled clipping (i do this with G Clip which is a free plugin in the mixing stage only).
- Parallel compression (mostly on drum loops, always leave out the kick don't like how it sounds on there).
- Most processing is done in the mix.

It's not a bad habit, there are tons of producers that mix into a ozone preset or some mastering chain. As long as you shape your mix in a way that benefits that preset than why should it be wrong? Perhaps it´s just the extra loudness that preset gives you what you perceive as good?

Personally i mix without any plugins on the master channel and try to make it sound as loud and as good as possible with no processing. I just don't like having a mastering preset colouring my sound before i start mixing. In the end i just add what's needed. Most of the time I only do some minor EQ adjustments and add a tiny bit of compression to gain some extra loudness and cohesion with a limiter in the end. I'd also like to add that in my experience most heavy processing is best done in the mixing stage and not on the master channel.

I think it's just a matter of taste and what suits best in your workflow.

Use reverb and cut off high end works for me Creates a "far away" effect in the mix.

In my own experience i find that a lot of problems can be solved/avoided musically instead of using all kinds of mixing techniques. If you keep layering and layering instruments and when they all have to fight for the same space then the sounds can get lost and it will sound like a hotchpotch. Same goes for the kickdrum check if its in key with your song, maybe you need a kick with more harmonics in order to punch through your mix. You can add parallel distortion to your kick in order to add harmonics. If your happy with the sound of your mixdown but the kick doesnt stick out very distinctly then maybe Dynamic EQ/Multiband Expansion will help to get the result you're looking for.