To become an assembly programmer understanding instruction encoding is not essential. If you were programming like the first computer http://www.imsai.net/ I had that had 8 toggle switches for instruction and 16 switches for addresses and then a button to write, this information would be critical
Fortunately, assemblers and compilers take care of this tedious business for us, so just glance through that chapter.
Thank you for replying, would you also happen to know if boolean algebra is a crucial part to learning assembly?
Depends on the type of applications. There is a definite advantage when working with PLC's or Distributive Controls Systems. To be an effective programmer you must know the processor your working with first, then the language of your choice whether it be NASM, YASM, FASM, GAS, MASM etc, and then the platform be it Windows, DOS, Linux, Unix, OSX. Then you will utilize formal skills that are application specific like algebra, trigonometry, calculus and so forth.