Azimuth angle is the angle measured between the top of the phono cartridge body and the record surface when viewed from in front of the cartridge while the stylus is in the record groove. If the cartridge is perfectly level, the azimuth angle is zero (0) degrees. If the cartridge leans to the left a bit in the counterclockwise direction, the azimuth angle is positive; if it leans to the right, the azimuth is negative.
Here is an illustration of azimuth angle:
Due to manufacturing tolerances the stylus may or may not be at the ideal orientation to the record groove walls when the azimuth angle measured is zero. This can be due to a variety of things, including the orientation of the stylus shank mounted into the cantilever, the alignment of the coils inside the cartridge, tracking force, and so on. Antiskating force can play a part as well.
We perceive performance to be best when phase response error between the channels is minimized, often at a similar azimuth setting where crosstalk levels between the channels are minimized.
This is a very complex question. Clarity, detail retrieval, frequency response, and record and stylus wear are but a few things affected by stylus shape, also called stylus profile.
Here are some examples:
Rather than repeat what has already been written on the topic, here are some relevant links:
The cartridge manufacturer specifies a range for recommended tracking force, based upon physical characteristics of the cartridge such as suspension stiffness, cantilever and coil mass, etc. It is best to set it according to the manufacturer's recommendations for best tracking. Too little tracking force, and it could mistrack and not sound balanced. Too much, and record and stylus wear could be affected and the coils will not be centered in the motor assembly inside the cartridge.
Antiskating force, also called bias, is used to compensate for the tendency of the tonearm to seek the center of record. Antiskating mechanisms most often employ small weights to apply slight force to the tonearm to push it outward. Some tonearms use a magnetic antiskating mechanism. For conventional gimbal type arms you often set it based upon the tracking force used. Unipivot arms may require little or no antiskating. There are at least a couple of methods for setting the correct amount of antiskating force, the results of which are properly centered image and good tracking across the record.
VTA is the angle measured from the cantilever pivot point to the stylus tip and the plane of the record surface. SRA, which is what counts, is measured between either the centerline of the stylus shank or the rear edge of the stylus (depending upon stylus shape) and the plane of the record surface.
An excellent article from a 1981 issue of Audio magazine, More Than One Vertical Tracking Angle (PDF), covers the topic well.
Michael Fremer has written articles on these topics: