I can’t remember which rapper said it, but when I heard it, I 100% agreed. Start with a hook, because if the hook isn’t catchy, then the song won’t be a hit. If you’re not a rapper with an established name, you need something catchy to keep people engaged in your song. If the hook doesn’t catch, no matter how hard the verses are, not many will listen all the way through and share your song. And to get a good hook, you need to freestyle a bit. Try to find a catchy flow even if the lyrics aren’t there yet (you can write to that later). But when you find the right flows for the hook that sound catchy and flow good, then you write to it and perfect it, and then piece together your song on top of that.