What angle should I set the VTA on my VPI turntable?

My cartridge is a Lyra Kleos.  I believe VTF and azimuth are good.  I use a digital scale for the VTF and use both (i) a bubble-level and (ii) a super-light aluminum bar/old fashion ruler to adjust azimuth.  Those settings never change.

So based on the responses above, starting with the arm 100% parallel to the record surface sounds like is a good place to start.  Presumably, the stylus is sitting at a perpendicular angle to the record surface.  I recall reading somewhere that the optimal SRA is 92 degrees.  Two degrees off ... screw it.  Close enough.

Any further comments or suggestions on VTA????  Lewm ... you out there??

P.S. -- I am listening to Linda Ronstadt singing the old classics accompanied by the Nelson Riddle orchestra; the record is part of a 3 record set.  Boy oh boy, ... can LR handle a song.    

Ok, ... so I just set the tonearm to be 100% parallel to the platter.  Then I closed my eyes and started to adjust the VTA up and down.  There were subtle changes in the sound as the folks above described. 

So I kept adjusting the VTA up and down until I found what seemed to be the sweet spot.  The playback had good detail and the bass was taunt.  I then re-checked the VTA with my bubble-level.  Surprise, surprise.  The arm was almost parallel to the platter with the pivot side very slightly raised.  Go figure.  I guess I just like sonic swill.  ;)         

Thanks guys.  If jcarr catches this thread, maybe he can weigh in with some practical advice since I am using one of his cartridges (Lyra Kleos).  

My sense is that lewm's approach makes the most sense.  I ordered a cheap super light/small bubble-level to double-check the azimuth and VTA one more time.  I will probably tweak the tuchus (the backside) of the arm up a smidge and call it a day.   

While I can envision that raising or lowering the tail of the tonearm will affect VTF and the P-S distance to some degree, I surmise that a small adjustment of the VTA wouldn't make all that much difference in SQ.  I am not OCD about my turntable and do not have the patience to make a minute adjustment to VTA and then readjust the P-S distance and VTF.     

Just for kicks and giggles, I bought an Elvon "LP Vinyl Record Player Measuring Phono Tonearm VTA/Cartridge Azimuth Ruler."  The kit comes with a super light and super small bubble-level.  Dirt cheap too.

I also rooted around for the box and instruction that my Lyra Kleos cartridge came in.  Lyra recommends that the tonearm be parallel to the record surface and then small adjustments from there.
 
To my surprise, using the cheapy Elvon azimuth ruler and bubble-level, it turns out that my VPI tonearm was slightly out of adjustment.  Azimuth was off by a teeny amount and VTA was off by more than a small amount.  So I adjusted the tonearm and double checked the VTF.  I tried to compensate for the weight of the bubble-level too (about .25 grams).  Although not perfect, I checked my adjustments with the azimuth ruler and then double checked VTF and azimuth again with the bubble-level.

After all is said and done, I think my tonearm is for the most part parallel to the record, but I lifted the back-end by a smidge.  Hardly noticeable on the bubble level.  I thought the lift improved the sound.  It also was a rough justice compensation for the weight of the bubble-level.

After fiddling with the adjustments, I played some favorite LPs and was pleasantly surprised.  There were noticeable improvements in imaging (real sharp), soundstage (better centered and less smeared) and SQ.  All around noticeably better.