As somebody who's been learning about 6502 internals recently, this web page has been incredibly helpful. It's not a silver bullet, there's a lot of instructions that don't fit the pattern, or they do fit the pattern and there's only one or two of them so there's little point, but for the most regular operations (Group 1: ORA, AND, EOR, ADC, STA, LDA, CMP, SBC) it makes things so much easier.