For TOS: Whatever is depicted or stated the majority of the time AND/OR fits in with the original movies is what's correct. "James R Kirk" is incorrect. "United Earth Space Probe Agency" is incorrect. References to TOS taking place in anything besides 23rd Century are incorrect.
For TNG: In a continuity debate between Season 1 and the rest of the series, the rest of the series is correct.
For the TNG Movies: In a continuity debate between Film Trek and TV Trek, TV Trek is correct.
Anything related to Trills, Bajorans, or Cardassians: DS9 is correct.
For Voyager: "Threshold" is non-canon. Everything else is canon but I look at continuity issues on a case-by-case basis to decide which version is correct. The depiction of the late-third season in the fifth season's "Latent Image" is incorrect. As good as the episode is.
For Enterprise: The Prime Timeline and the Kelvin Timeline are both possible futures. 2233 is the fork in the road.
For the Kelvin Timeline: It shares ENT with the Prime Timeline. Ambassador Spock is from the Prime Timeline. Anything that happened differently from 2233 on is the result of Nero and the Butterfly Effect.
For TNG: In a continuity debate between Season 1 and the rest of the series, the rest of the series is correct.
For the TNG Movies: In a continuity debate between Film Trek and TV Trek, TV Trek is correct.
Anything related to Trills, Bajorans, or Cardassians: DS9 is correct.
For Voyager: "Threshold" is non-canon. Everything else is canon but I look at continuity issues on a case-by-case basis to decide which version is correct. The depiction of the late-third season in the fifth season's "Latent Image" is incorrect. As good as the episode is.
For Enterprise: The Prime Timeline and the Kelvin Timeline are both possible futures. 2233 is the fork in the road.
For the Kelvin Timeline: It shares ENT with the Prime Timeline. Ambassador Spock is from the Prime Timeline. Anything that happened differently from 2233 on is the result of Nero and the Butterfly Effect.