A rap song is different from other conventional songs. A rap song generally has much more lyrics than any conventional song would ever have. And this is in fact a major reason why people love raps. Raps bring focus to the words. Raps bring focus to the storytelling, to the ideas that they represent or to the feeling that they want to express. A good rap, therefore, is about telling a story or expressing a feeling in a musical way. In a way that gives those words a rhythm of their own. To some extent raps are like poems, but with an informal way of narration and with cheerful musical beats. And therefore writing a good rap is not child’s play.
If you want to make your own rap, a good and easy way, to begin with, is to have a beat first. Have an initial music beat to guide your thoughts. Then let your brain run freely. The best of ideas are those that pop up out of nowhere. You should keep a broad topic in your mind about which you want to write, but for finding the right words, don’t focus too hard, just let your creativity run wild. Let some initial ideas come to your brain. Try to put your ideas into a beat and in a rhyming scheme. Let several beats and rhymes come to your mind. Note down ideas as and when they come and after you have some good amount of words and rhyme ideas, do some brainstorming sessions. Try to expand your word ideas and develop a story out of them while keeping them in sync with a rhyme. You should soon have a good piece.
Keep listening to this initial piece you have made, again and again, make improvements in your lyrics, choice of words, metaphors, rhymes, music beats and whatever you can do. Also let some of your friends listen to these songs and give their own ideas. Finally make it public when you have a perfect piece.