I am experimenting with VSTs lately to try to make some nice bass presets I can use (LMMS doesn't have many). So do you have tips on how to make a nice basic bass? I experimented a lot, I usually took a sine wave for the base bass, and then stacked triangle, saw wave, etc. and experimented with oscillators with many harmonics. At the end I applied usually a low pass filter, to soften the harsh harmonics. While that procedure was kinda -ok-, the bass sounded rather flat and without depth. It hadn't this 'crispness' and thickness like the basses I hear in various songs.
I have never been able to do this. I suggest trying to use a real bass guitar or string if you can. I seen a great bass made from a mop handle and washtub played with a work glove.
What ever you have [digital samples] you can try to use the Equalizer to adjust the low frequency and cut out others so each instrument has its own "space" for clarity and you can also try using the spectograph sometimes that helps when your hearing isnt developed proper.
If your using zynaddsubFX try adding the banks filepaths for Yoshimi those are great.
In LMMS have you used the LFO controller this signal is a low frequency oscillator it is used for controlling pan for phasers or volume if you want but perhaps you can do a ring mod on it or use it in other manners. PS if you use yoshimi open it up and copy the file paths for the banks and put those in zynaddsubFX for LMMS's vst plugin to use. It basically adds yoshimi to zynaddsubFX.
Consider low pass filter so separate your bass sounds and high pass for the other instruments like Trumpets etc. Some sound cabinets do this its called a "crossover."
Try animating the filter with an envelope generator with a snappy attack, adjust decay and modulation depth to taste. Keep the cutoff frequency relatively low, using the envelope to shape the frequency response - this will let you balance a punchier attack with a deeper bottom end in the decay/release. If it gets too clicky, increase the attack time a bit.