"Respect & play true to the source material" is pretty much the rule.
As for canon and continuity- Canon is subjective, and different for everybody. Some franchises have a single spokesperson who decrees what it is, and others don't, but in any case every member of the audience has their own canon.
For continuity, I think Dr Who legend Terrance Dicks said it best- "Continuity is what you can remember at the time"
Isn't it "personal continuity" that's subjective? Doesn't "canon" mean core body of work, which in the case of Star Trek
is the onscreen material?
It does- but individuals' definition of what constitutes the core body varies, especially when there isn't a single official authority to define it officially.
When you don't have an authority who dictates what is considered to be the core body, then everyone else can and does determine that for themselves- personal canon