Rap has to face the lyrics that are improvised and freely played. If you want to rap or write meaningful lyrics, you need to read more books, have a wide range of knowledge, react quickly and have strong logical thinking ability.
If you want rap to sound good and catchy, you should rhyme with the words in the poem. Simple and easy to use is the rhyme of the last word of a sentence. Of course, there are many forms of rhyme. There is no need to rhyme deliberately, and the content will always come first.