I agree with what most of Artur Rutra writes. Especially ,as I've already stated, the need for experimenting. It reall y pays off later on.
And you can tell that you are becoming really  "renderized" when you see something in the real world - be it a sky or a spot in a forest - and you go "...well...just a little more haze and radiosity gain, then it would be perfect..., and perhaps a little less cloud densitty, also..." or something.  (This has been up several times before in the forum, well here it is again G.).