In pretty much any writing medium (novels, screenplays, short stories, etc), standard advice involves hooking the reader within the first paragraph or so. This is partly why "in medias res" tends to be such a popular opening technique - it drops the reader straight into the action, which is theoretically more interesting than "She woke up, got dressed, and went downstairs for her daily breakfast of toast and juice...". However, starting in medias res has itself become something of a cliche, to the point where you have to really know what you're doing to be able to use it effectively.

What I think a lot of novice writers, and people giving advice to novice writers, often miss is that "hooking" your reader doesn't mean immediately assualting them with action. All it means is raising a question the reader wants to know the answer to.

For example, "The Wizard Hunters" opens with the line "It was nine o'clock at night and Tremaine was trying to find a way to kill herself that would bring in a verdict of natural causes in court, when someone banged on the door." Not much action - Tremaine is sitting in a dusty library reading books - but that line raises two immediate questions: 1, why is Tremaine trying to kill herself in a way that would be ruled "natural causes", and 2, who's banging on the door at 9pm?

Similarly, "Black Sun Rising", the first book of the Coldfire Trilogy, opens with the line "She wondered why she was afraid to go home." Again, the line raises multiple questions, inviting the reader to keep reading to learn the answers.