It seem obvious, but rarely applied: Use the book! If a fact or event is specified as one way in the book, then it is rarely better to alter its depiction. For Example: Having Marianne pike off toward Combe Magna to get dramatically sick is not supported. Cairen Madden [S&S0] and Tracey Childs [S&S1] did not need that schtick to portray Marianne getting sick on the way to Cleveland from her chronic self abuse.
Two: Intercutting between two possible congruent events [S&S3], as the sword fight/Marianne's writing a letter, may be, but one started first, stay with that one until event complete, then do the other. That was incompetent editing. Not everybody is on goof balls and some consider the flickering images to be visual assault and eyeball battery.
Three: Go easy with the orbiting cameras. Only ONCE have I seen it NOT done to a total pig's breakfast [Babylon 5, season two, "Comes the Inquisitor"].
Four: If the script and the shooting put more than two good hours in the can, then use it. Parse it out into a sequel or a more extensive mini-series. If the story is coherent in 3.5 hours, then charge about twice the admission. Do not take a good script, good acting, good cinematography, and then ruin it with buchery to keep some arbitrary and capricious length; especially when the closing credits tend toward ten minutes (some have used two or three theme musics at the end) long.