When rapping to a beat, do u copy the instruments or rap over them?

I've got a problem when rapping, i dont know what rythm im suppose to be following,
at the first few seconds of this you can see im just copying the trumpet thing, but then i sort of jus rap a completely different rythm over it, because i thought just copying the trumpet the whole way would be boring, is this the correct way to rap to the beat?
just place ur own rythm over the top?
kinda confused...
When rapping to a beat, do u copy the instruments or rap over them?
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