Hooking the reader in may be one of the most important aspects to a story.
They should be well thought about like themes you've briefly and subtly indicated, for example.
If there's no hooks, writing sound's plain.
And you need to have readers hooked in from the first paragraph; the first sentence and even the first word.
You can use short sentences. Contrasting with longer, descriptive sentences.
Opening paragraphs should stir curiosity and interest in your reader.
Build up suspense and maintain it.
Hooks make questions arise with a need for the answers.
It's your choice as the writer, when you give out these and how you convey them.
It's your choice when you drop the bombshells.
Hooks should be evenly distributed to avoid bland 'filler' chapters.
Having abrasive characters that don't completely get on with the narrative character/s will mean they'll put pressure on the protagonist, who's then more likely to reveal plot hooks.
All in all, hooks are essential for a successful story.