Leveling your turntable, your approach?

I would have to believe that the most important factor in "leveling" would be to make sure the platter was rotating around the axis perpendicular to the vertical axis of the bearing. Imagine extending the vertical axis of the bearing and proving perpendicularity with the horizontal plane of the platter.
This same logic would also apply to the pivot point of the tonearm.

I used to use a level and go side to side, front to back, and corner to corner. Now I use a circular bubble level. It is easier and I believe it has better accuracy because it shows 360 degrees.

Do your main bearing a favor in the long run and level the bare platter with an accurate level and/or levels.

I use selected bullseye levels that cost all of $2-$3 each.

The levels were hand picked by placing them on a sheet of plate glass which had been leveled with expensive/accurate carpenters levels.

Think I went through 50, or so, to find 3 that looked good.

The local Mom & Pop hardware store let me use their high end levels, plus a sheet of flat glass (been shopping there since the 70's).

I'd guess that measuring even keel with various LP's will give various results.