Hook
A hook is the opening passage that gives a reader a reason to continue — a question raised, a character worth watching, or a situation that has just changed.
Sol Stein watched browsers in bookshops and found the pattern brutal: most read the jacket flap and then went to page one, and almost none got past page three before either taking the book to the till or putting it down for another. Agents read the same way. The hook is not a flourish, it is the audition.
Stein's goals for a first paragraph are modest and testable: excite curiosity, preferably about a person or a relationship; establish a setting; lend the story resonance. A longer working checklist for an opening — does it raise a question, introduce a vivid character, surprise, change the existing circumstances, create immediate danger, build a sinister atmosphere, or leap into action? — is best used as a list to fail against. An opening that ticks none of those is not slow, it is inert.
The most common repairable fault is a first page spent orienting the reader. Description of the room, the weather and the family history is the writer getting comfortable. Start where the circumstances change and let the reader assemble the rest, or open in medias res and supply the background once there is a reason to want it.