Hello. I'll try to help.
First you need to read up on poetic metre
I recommend reading the entire entry and then maybe also the entries on iambs and trochees. In short the metre is the pattern of unstressed and stressed syllables. Here's an example from the entry on trochees:Should
Try saying it out loud. Notice how it has a rhythm caused by alternating between stressed syllables and unstressed syllables? It sounds like DUM-da DUM-da DUM-da DUM-da.
Now try saying that sentence fast.
Now try saying "Conglomorates tax working folks" equally fast. I'm assuming you can't do it. I can't. The sentences have the same number of syllables ( 8 ) but the former is much easier to say fast than the latter. Why? Because the rhythm in the latter sentence is "wrong" for saying fast and the rhythm of the former sentence is "right."
Now listen to the fast part of Eminem's 'Rap God':
- Eminem wrote:
- Uh, summa lumma dooma lumma you assuming I'm a human
What I gotta do to get it through to you I'm superhuman
Innovative and I'm made of rubber, so that anything you say is
Ricochet in off a me and it'll glue to you
And I'm devastating more than ever demonstrating
How to give a motherfuckin' audience a feeling like it's levitating
Never fading, and I know that haters are forever waiting
For the day that they can say I fell off, they'll be celebrating
'Cause I know the way to get 'em motivated
Try to say it slow and hear the rhythm. Notice something? Eminem is also alternating between stressed and unstressed syllables, which is what allows him to say those words at the speed he does.
Now, alternating between 1 stressed and 1 unstressed syllable isn't the only rhythmic pattern you can rap fast, but it's the most common one. It's a good place to start.
Also it's not the only thing required to rap fast. You also need to make your mouth move fast enough. That comes only through practice. Tongue twisters are especially helpful. Try finding some on the internet and practice saying them faster and faster without messing up (or rap along with Eminem, Tonedeff, Twista etc.) If you start writing rhymes in a suitably rhythmic pattern, you might also find there are simply some words that always mess you up when you try saying them next to each other no matter how much you practice your rap. Consider rewriting then. There's no shame in it. All fastrappers write their verses specifically so that they
will be able to say them fast. Eminem couldn't necessarily rap Tonedeff's verses, and Tonedeff couldn't necessarily rap Eminem's. Write it so that you can say it and if you can't, consider rewriting.
Hope this helps and gets you started.