Official Website of The Game and Roley Boyz!
One easy thing you can do is dissect the lyrics of your favorite songs. Say your favorite rapper is Game. Go look up the lyrics to your favorite Game song on Google.
From there, see how he pieced his words together. Try to get into his mindset. Ask questions like "why did he do this" "why did he say this here instead of there" "did this make since or did he say it just to make it rhyme"
Those are ways that can help you start off. Hopes that helps! :)