A good rule of thumb that i go by is this:
If the leaf isn't covering a bud location, leave it.
A lot of my friends seem to think i defoliate too much, but the truth is, a decent amount of people don't defoliate enough. Including them. I hear them complain about how half of their harvest was scurfy popcorn nuggets, while i'm breaking up my nice and dense buds.
It makes me chuckle, especially considering i've told them to free up more light for the buds a million times before. They just seem to think that, eventually, not defoliating will work the way defoliating does. Textbook definition of insanity.