Well, they often introduce a mysterious or alluring character right away. For example, 'She had eyes that held a thousand secrets, and he was determined to unlock every one.' It makes you curious about the woman and the man's intentions.
Well, they often create intrigue. For example, the opening of 'The Great Gatsby' - 'In my younger and more vulnerable years my father gave me some advice that I've been turning over in my mind ever since. "Whenever you feel like criticizing any one," he told me, "just remember that all the people in this world haven't had the advantages that you've had."' This makes you curious about what that advice will lead to and what kind of story the narrator has to tell. It's like a hook that pulls you in.
Some best opening lines set the mood. Take 'The Road' by Cormac McCarthy: 'When he woke in the woods in the dark and the cold of the night he'd reach out to touch the child sleeping beside him.' This line gives a feeling of desolation and a sense of the bond between the characters from the start. It makes the reader want to know more about these characters and their situation.
Another way is by setting an unusual scene. In 'Slaughterhouse - Five' by Kurt Vonnegut, the opening 'All this happened, more or less.' gives a sense of ambiguity right away. It makes the reader question what 'this' is and how it happened'more or less'. It's a unique way to start a story that is full of time - jumps and surreal elements.
Great opening lines often introduce an element of mystery or intrigue. For example, in 'The Hitchhiker's Guide to the Galaxy' with 'Far out in the uncharted backwaters of the unfashionable end of the Western Spiral arm of the Galaxy lies a small unregarded yellow sun.' It makes you wonder about this strange, uncharted place.
Some opening lines use shock value. Like 'All this happened, more or less.' from Kurt Vonnegut's 'Slaughterhouse - Five'. It's a rather nonchalant way to start a story that is about the horrors of war, and this contrast between the casual tone and the serious subject matter grabs the reader's attention.
By introducing an interesting character situation. 'Ava, a simple farm girl, found a strange amulet in the field one day. As soon as she touched it, a voice whispered secrets of a far - off land in her ear.' This makes the reader want to know more about Ava and the amulet.
They often introduce an emotional state. Such as 'She was broken - hearted, but then he came along like a ray of hope.' It makes the reader care about the character's emotional journey.
They often start with something unexpected. For example, in 'Charlie and the Chocolate Factory', 'These two very old people are the father and mother of Mr. Bucket.' It makes you wonder who Mr. Bucket is and what the story will be about.
They create mystery. For example, a line like 'The man in the black suit came early in the morning.' makes you wonder who the man is and what his purpose is. It hooks the reader right away.
They create intrigue. For example, the opening line 'Call me Ishmael.' from 'Moby - Dick' makes readers wonder who Ishmael is and what his story will be. It's a simple yet effective way to draw the reader in.