I usually start with the bottom of the cartridge parallel to the record and go from there
I've read that most guys start from zero and adjust vta by ear. If I like the sound with the pivot end slightly lower than the cartridge, as long as there is sufficient clearance between cartridge and record, is this a problem? ( ie excessive wear on the bearings?) I have read that some prefer such a setting.
The problem is "what is parallel". SME has the perfect answer on the V with a horizontal line silkscreened on the arm itself, however, absent that line with other arms, its all listening and evaluative. Fremer suggests that a microscope and computer program be used to determine the angle of the stylus...a very complicated and exhausting effort. For me, there really is no answer...I set my arm that has a significant tapper so that the bottom of the arm is going uphill a bit. I am confident that I have not coaxed the ultimate sound from this adjustment, however, I am also confident that I will never be satisfied and have to restrain myself from tinkering my life away on this. I love the sound of my setup and just have to be satisfied with it until my unrest that "maybe" I can get more from the arm" will overcome me yet again....yet another disorder I have to suffer from.
As several have noted, if you're just looking for a starting point then any reasonable point will do. Armwand level is reasonable. Bottom of cartridge parallel to record surface is reasonable. Spending 4 hours with a microscope and spot light is... reasonable if you prefer that sort of thing to listening to music.
The fine tuning, if your ears tell you it would be beneficial, must be done on an individual LP basis by listening with educated ears. Precisely where you start from is of little consequence, so don't fret what doesn't much matter.