As always lots of good advise...
My understanding is that like most photography and processing and printing disciplines it comes with experience and practice.
When I was taught I was always told to under and over, could'nt be simpler... meter, set as meter then two more images one stop under and one stop over...
The more cynical of you would say thats a great way to chew up lots of film....and what does Simon do......make film !
Seriously I know photography is not a cheap passion...but there is no substitute for a good neg, never has been, never will be, and when you are starting out this gives you a much better chance to get a good neg and not to become frustrated.
and I still occasionaly under and over.
Simon ILFORD Photo / HARMAN technology Limited