When you write the first verse of your song, you want to slowly introduce the listener to the content. Sometimes, in the early days of rapping, you want to hit the track and you want to go rapid fire and show people how good you are. But the majority of the world are not connoisseurs of rap, so you want to start off slow and take people on a journey.
So, you give, actually, less words and put a little bit more space in between your words, so that you take your time in the first verse, especially if you're telling a story-type rap. You want to introduce people to the character before you get to the conflict. You want to give them a sense of knowing who the story is about.
If you're doing a bragadocious kind of rap, you're just talking about yourself, you just want to start off by introducing your name, saying your name a couple times in the verse. Saying where you're from. Just introduce people slowly in the first verse to introduce who you are and what the subject matter is about. And that's how you write the first verse.