A hook is the most appealing part of the song; it catches the listener's attention. In rock, hip-hop, dance and pop music, the hook is usually found in the chorus. It can be a phrase or rhythm or both, but if it includes words, it should suggest the main theme of the song. There isn't a secret formula to writing a catchy hook, but you can try certain things to inspire one.
Listen to masters of the catchy hook like The Beatles, The Beach Boys and The Ronettes. Take note of the types of words these artists use in their hooks, the number of syllables in those words and the common features of the rhythms.
Compose the hook using notes, scales and intervals you're comfortable with and enjoy. Your familiarity with these sounds will help you develop the hook.
Use different types of intervals for the hook to make it stand out. For example, if the majority of the song is in a third or fourth interval, write a hook that has a leap of a third or fourth.
Keep the hook short. Whether you're using a phrase, a beat or both for your hook, make it short enough for audience to remember it.
Repeat the hook a couple of times in the chorus. Repetition will lock the hook in your audience's memory.
Play the hook to a friend or a musician before you play the song in front of an audience. Ask that person to critique the hook and offer any suggestions for improvements.
Abandon the hook during the song's bridge. This will leave your audience waiting in anticipation for the hook.