This method works best for freestyle rappers: Start by selecting the beats you'd like to use for your rap and preparing to perform the rap into a voice recorder.
Start the voice recorder and perform the rap.
Play the rap back on the voice recorder and transcribe the words onto paper. You may need to slow the speed of the rap on the voice recorder in order to be able to write down all of the words onto your sheet of paper.
Add line breaks to your rap, where appropriate.
This method can be used for planning a rap performance: Start by selecting the beats for the rap.
Identify the rhythm of the song and pick a corresponding rhythm for the words.
Select a topic to rap about and listen to the rhythm of the music as you write the rap on paper.
Perform the rap to check for inaccuracies and make any changes to what you've already written on the paper.