I think is most powerful tip is to decide really what instrument or sound should be playing the below 80Hz or so – which are the lowest two octaves.
The best option is, if you have only one instrument playing, like a bass or a kick. Usually it’s not possible or the case, as a kick doesn’t give you a “sustain”, which actually defines the real “beaf” down there.
Example A: Kick and a 808. I like to give the Kick more “Click”, more punch, which makes the Kick shorter as well. You can either do it by using a compressor with slow attack, around 40-50ms, or you take the “Transient Designer” approach and reduce the sustain/increasing attack. Doing this, you give the 808 instantly more space to live in. The 808 should be ducked, either by a side-chain compressor, 3-10dB, depends on the sounds and the sound you want to achieve. You can take a ducker, which reduced the volume by a couple of dB. The great thing is you shape the volume-envelope, so it’s easier to make it sound as you like. Compressor does only give you the release, where you need to find the right ms time, sometimes it works well, sometimes it doesn’t. Another option would be using your volume-fader and draw the curves. A lot of work, but you can copy-paste. Last option, which comes to my mind right now, is using a dynamic-eq, which is more precise in terms of EQ-space. What you can try do is, using ALL at the same time, but more sparely, so 1-2 dBs here, 2-3 dBs there. Can work wonders and sounds even more “musical”.
Example B: Trailer Music – Let’s say you want your drums, all of them, have the greatest impact at the final climax. The same thing: As you can probably have 10 drums, which have too low-end when combines, you need to pick only one of them, as your “main character”. All other will be ducked by this character. As in example A. If you have a well thought-out template, you will usually see this: 1. Bus is your Kick, 2. Bus is your Bass or Low-End, and so forth. This gives you the option to use side-chain triggers, so you can really “control” your mix.
Another options: Let’s say you have a great bass-patch, however you think that it’s just too much “unclear” low-end with a lot of saturation, dirt, etc. You can A: take one of the oscillators and change it to a clear “Sine-Wave”, or B you cut the low-end and use a clear sine-wave as a layer track. The problem for sub-woofers is always to move this heavy low-end, which is really difficult for the speakers to handle, as too much uncleared frequencies are playing at the same time. The sub is basically “distorted” 2x times. By your sound and by your sub-woofer. So this “clear” sine-wave option can work wonders as well.
Saturating low-end doesn’t make sense, as I said before, only if you want to achieve a certain sound. However if you saturate the first octave of the bass (creating rich harmonics), your brain thinks you have “more” low-end actually. This is fact, as this is how our brain works. That’s the case why everyone wants to hear the low-end on smaller speakers. You trick your ear/brain that you have more, but actually you don’t.
But all above are only “tricks” for mixing. If you want to make something even more “clean”, you just need to adjust your arrangement and decide really, where and how certain things should play and sound. Arrangement is your second friend for your great productions. The first one is using already great rich sounding samples, where you don’t need to layer anything else to sound even more “awesome”.