I recommend this alot, so I think I will again: If you're a total beginner to programming, check out:
Assembly Language: Step by Step, by Jeff Duntemann.. The catch here is he teaches x86 asm, not 6502, but if you teach yourself just a tiny bit of x86, you could easily pick up 6502 as all of the concepts are common to all assembly languages.
He actually says in the opening pages that the book is aimed at total beginners to programming. When I read it, I was not a total beginner, so I don't know how true that would be, but I do know that when I read it I needed something to hold my hand in order to learn assembly language and that is exactly what he does. So, I'd highly reccommend it, even though it is a somewhat less than direct path towards NES development. Maybe it could help clarify some of the more difficult aspects of assembly programming, like hex, binary numbers, logic operations, etc.