I’m not a drone purist by any means, but I tend to use a lot of drone voices in my music. Like others said, I tend to set up voices and then control mix levels. I also like putting timbral controls or effect parameters under fader control.
I very much prefer to have some texture in my drones, rather than a completely “static” sound – so all the methods I use are designed around that. I use FM or PM quite a bit to get growly textures, frequency beating, and create opportunities for timbral changes. AM and RM can do the trick as well, as can filter FM. Wavetables can also be good at motion, though I often pair them with other oscillators for modulation. Running a polysynth through distortion to get intermodulation can also be rewarding.
I’m also very fond of resonators and delays, and occasionally granular or spectral FX, particularly in feedback loops. Or a pitch shifter and reverb. A compressor/limiter to keep levels under control but perpetuate the loop, and a shelving EQ or fixed filter bank, can really work wonders. Small EQ changes cause different chord voicings to emerge.
I bought a Lyra-8 recently and it’s a drone monster, although it also begs to be played in a semi-melodic way.
I do like ebows on stringed instruments, but I don’t currently have anything set up for that. It’s more something I enjoy in other peoples’ work. The tone can be a bit more static than I like, but that depends on what you do with it. I’m also a fan of the hurdy-gurdy but will probably never own one