As stated, your first ten pages should imbue the reader with an idea of your story's tone and initial conflict. At least one major character should be introduced (doesn't necessarily have to be the lead antag or protag). It should grab the reader and make them want to read more.
This next part is my own opinion:
It should be strong, but not the best sequence of the script. Horror legend Wes Craven has stated on numerous occasions that in his horror films, he wants to blow the audience away with a great horror sequence right off the bat, something which breaks a taboo. That way the audience says to itself, "If he's showing us this in the beginning, I can't wait to see what else lies ahead." The anticipation of worse horrors to come is what reels the viewer in and keeps their eyes on the screen or, in the case of screenwriting, keeps their eyes on the page.
Unfortunately, Craven's films en toto rarely exceed his opening sequences, but at least he's got the right idea lol