1. Fresh strings, or if you're cheap, boil them or use the "slap them against the fretboard" technique
2. Proper input volume
3. Modest onboard eq, I usually increase the treble and reduce the mids just a tad to make it clank better
4. Filter into multiple tracks a la Systematic. I find that the single biggest determinant of the bass tone is the steepness of the high pass and low pass filters you end up using here on each track, and what frequencies you set them to. I usually use an 18db/oct low pass filter at around 185 for my DI/low end track, with the HPF set to about 35 at either 6 or 12 db/oct. Sounds extreme, but those low mid frequencies are absolutely useless and you can add them back in in a more controlled manner by reducing the HPF of your clank/distortion tracks. Speaking of which...
5. Clank/distortion tracks! Whether you use just a DI and a clank, or a DI and distortion, or all three will substantially alter the tone. Try inverting the phase on each track to see what sounds best to you- you will often get phase cancellation when you distort the tracks. I usually use a DI, a SansAmp track, and a Dual Rectifier track. Your HPF/LPF determine how much of these tracks you can use in the mix. Lower HPF = muddier bass tone that sticks out in the mix. Lower LPF = making the tone less present, but it also tends to blend better with the guitars/drums/vox and allows you to turn up the overall bass volume a bit more.
5.5. Relative volumes of the 2-3 tracks. I mute the clank/disto tracks and set the DI volume to 0, then bring it up until the mix feels full. Then I set the disto/clank tracks to 0 and bring them up until you can just barely hear them in the mix.
6. "Character" EQ after your initial HPF/LPF decisions on the bus. I almost never boost, and if anything, I cut a little more around 200 hz to get rid of that nasally, whooshy zone from about 200-350 hz. Totally awful. Just be conscious of how much you're doing; if you use an extreme high pass/low pass on the DI, you shouldn't need basically any EQ on the bus at all.
7. Compression: where, how much, what type. I always have a modest amount of Waves bass rider on my DI (even after doing some manual volume riding on the track itself), followed by gentle feedback compression like the TDR Feedback Comp just to smooth it out. On the bus, I usually have 2-3 db of gain reduction from a medium attack, slowish release SSL compressor, then an 1176 just to catch the peaks, then a limiter to catch any last volume jumps. Multiband compression can help, but it's easy to mutilate the tone by accident if you have each segment solo'd, so be careful.
8. Saturation/distortion/whatever on the bus. SoundToys Decapitator is good from what I've heard when used sparingly; I usually use a bit of Reaper's JS Saturation plugin and Slate VCC set to either the US or Brit N. Play with the drive to get to the point where it starts to muddy the sound then back off. This should add some harmonic content to a very surgical-sounding end bass tone and make it sound more natural.
I'm by no means an expert, but I've always struggled with bass tones as well and I've found these to be the most important parts of the process. The new version of Ermz' guide has some interesting techniques involving using saturation at an earlier stage in the process, and different compression ideas. Overall, you can sort of fuck everything else up, but you have to get your HPF/LPF frequencies/slopes right, and you have to know how to use a compressor well. Everything else should fall into place with some modest effort.
