The hook or chorus lines should depict what the song is about. Sometimes the hook will even duplicate the title of the song. Take the Elvis Presley song, "I can't help falling in love with you." The title is also used in the chorus. This was a huge hit!
The melody for the hook should blend with the rest of the song so it doesn't sound like two different songs once the melody is changed over for the chorus or hook lines. But there should be a change. Usually an upbeat or brighter notes will work well in brining attention to this important part of your song. Additional energy should be installed here.
The amount of beats or syllables should be consistent with the previous and proceeding beats. In others words, if you just came out of 10 syllables or beats for your last lyric line, you don't want the number of beats for your hook to be much longer or shorter than that. You want to gain attention here, but you also want to stay within a flow.
Your hook or chorus should rhyme and make sense. Words that tell the whole story in very few words. It is okay to run two parts or sentences also, one directly after the other. An example may be, "I thought I had a lover and a Friend, Till I found out all you did was pretend." This hook tells a quick story that rhymes. In this example both parts have 10 syllables.
The hook should be easy to sing along with, and ideally in a middle key or note, so that anyone can sing with it, and at least be close to being on key!
The hook should be one that anyone would not be ashamed to sing along with out loud. When writing a song you want it to appeal to the greatest number of people, thus, your hook line should be as universal as possible. When reaching both males and females for instance, you may not want your hook to be something like, "you say I'm a tough guy, and I just don't know why." Would a woman want to sing along with this hook? Of course when a writer wants to reach a specific group, the hook should be aimed at that target audience.