Its actually not that much of an issue with TOS cuz they dont make a lot of references to past shows. If yer gonna do it in order tho, I would start with the first TOS pilot, The Cage, then the 2nd TOS pilot, Where No Man Has Gone Before, then The Corbomite Maneuver. This was the production order, if you watch in the order of how they aired you might wonder why Uhura is suddenly in a gold dress or why Bones is suddenly gone and replaced with a different doctor lol. Have fun!