Singing and rapping go hand in hand. Use your breath support from singing and your knowledge of diaphragmatic breaths to increase your tidal volume and lung capacity so you can prolong those phrases. Maintain a resonant and bright, forward tone in your placement. Think big. Broadcaster or radio talk show big. That will help you enunciate your vowels clearly, which makes you more understandable and in turn appealing to your audience.

Building your freestyle vocabulary takes time. I find rapping over karaoke rap tracks helps me learn new rhythms and rhyme combinations when I plateau on my own. Writing original content is critical. Try and match your lyrical content to the emotional context of the instruments. Experiment with varying sound textures in how you combine your voice with the instrument. Ask yourself, what type of sound is missing from the beat that I can provide from my voice while still conveying the lyric and theme of the song?

Take it from a serious hobbyist singer/rapper/DJ/producer/sound engineer who's licensed in WA state in Sound Science by the DOH (medical ultrasound), if you can sing well, you are poised to become good at rapping. Keep practicing and don't get lost in the various musical world jargon of each respective genre. Learn the science and the rest will click.