I'm no expert at plug reading but there are threads on the subject, basically you do a good power run, I think about 15-20 seconds, don't quote me, then kill the
Engine and coast to a stop, not sure if you can pop it into neutral but you don't want the Engine turning if you can help it. the area of the plug to read in down on the inside on the porcelain this is the area that tell what it's doing, the coloration on the plug will give you an idea of what is going on, tan is good, oily and carboned up is not good but also could just be an indicator that you need to change plugs, white is not good and if you see aluminum deposits, well you may need a new piston at that point.
I prefer to be on the rich side of jetting, it may not be running at it's peak performance but it also lives longer, you will notice a difference on those cool days that it runs better, that is better than noticing aluminum on your plug.
now if racing, then tune for max performance at the track and plan to rejet the next time out, temperature and altitude make a difference.
oh, what were we talking about? make sure you are not too lean to start with and you can be rich in one area of the jetting and lean in another, Zeroclient has some good info using an O2 sensor.