There are two parameters we’re adjusting for: perfect verticality of the stylus and perfect electrical balance in the generator.
First, adjust as close as you can visually, to get the stylus looking vertical under normal playing conditions. (Azimuth should be tackled last, after VTF, VTA and antiskate are all well dialed in).
Fine tuning to get the cantilever/generator exactly balanced has the sonic effect of reducing crosstalk between channels. As an example, I hear Wally makes his Analog Shop to actually measure this (I have not used his tools). That would give you actual measurements so you’d know you were as close as possible.
To set by listening, what you’re seeking is the tightest possible imaging. Some people hear it easier with a mono record. I’ve never compared mono vs. stereo, I just use whatever record is handy. Something well recorded with a good center imaged instrument or vocalist is best. It’s easier to hear imaging and directionality on higher pitched sounds than lower pitched ones, so if you choose a vocalist choose an alto or soprano, not Paul Robeson.
Make EXTREMELY SMALL adjustments. The adjustments for azimuth are the finest adjustments you’ll ever make on a tonearm. Tiny changes can take you from too far left to too far right and fly right past the sweet spot. If you think the VTF setting on your cartridge, whatever the brand is touchy, Azimuth changes are ten times touchier.
Fortunately they are also less significant, sonically, and it’s pretty much set and forget. There IS one optimal position for azimuth and once you’ve found it for a given cartridge you can usually lock it in and forget about it.