1. make sure its in the right key. its still a "note" . A lot of 808 basslines jump up an octave for some variation for a note or two, put those notes on a different track so u can EQ the high notes more specifically...2. Sometimes pitched down 808 toms sound really good ...like an octave or two down, instead of an actual 808 kick sample. I do this in a sampler. 3. listen to ur mix on a laptop, ..can you hear the "tone" of the 808? U can experiment with saturation or SLIGHT distortion to bring out the harmonics and tone of an 808 or sub bass. 4. 80-90% of of a good 808 is in the sample choice, or synth sound design- not in the processing, if u try to enhance crap with processing, ull just end up with that, enhanced crap. 5. Sometimes I use massive or sylenth to make an 808. Like "WTF" from the Twonk album or the Roots Remix sub was made in massive. no secret tricks. Its just a Sine wave with some pitch envelope, and some basic compression and eq. The mastering and drum bus processing did the rest. 6. I usually have another smaller shorter, tighter kick layered on my 808s and I use a slight bit of sidechain compression to glue the kick and 808 together ...if the layered kick has sub frequnecies its gonna sound WAY better if its in the same key as the 808. You can also find certain kicks that will sound good even if u take out all the sub frequencies. The layered Kicks on Swoop, WTF, Clarity Remix, for example have nothing below 80hz or so. I actually have a really hard time hearing pitches of drums that low, so I naturally gravitated to doing my kicks like that. 7. Get rid of the useless rumble on the 808s, a high pass filter can help clear out some unwanted ish below 40hz...Also, make sure no other elements in the track have any unwanted, or uneeded sub frequencies that are gonna interfere with your 808. for example, in trap music, (GENERALLY SPEAKING) none of your other drums or synths or vocals need to have anything below 80 - 120hz ..sometimes they are there and you cant even hear it! so for god measure I put a HP filter on everything and sweep it to hear exactly what is going on, and the result is all my elements only have the lower frequencies they need, and nothing more ... get me ?8. Ok one more thing ... using "fades" on the waveform or region, I customize the decay of 808 to fit how long it needs to be ... so for example "on SWOOP, the 808s dont decay, its like just like brick, solid long note... but on Clarity, each note got its own decay ...

..here is a screenshot of my 808 and layered kick track for my Clarity Remix ..

Good luck, experiment and find your way of doing it and make some magic! A/B your stuff against tracks u think sound amazing and keep pushing your limits! hope this helps some of u, feel free to ask me questions.