Start slow.
Really slow.
What makes someone sound good when they are playing slap is how "neat" they are.
No open strings ringing, and notes starting and finishing when they are meant to.
Start with a song that plays mostly octaves, start slow, and build up speed.
Im assuming you know the basics of slap, like where to hit the string, how to position your hand?
If not, id have a look on youtube. Im sure Scotts bass lessons will have something useful for you.
Once you think you know where your going,
I think "treasure" by Bruno Mars would probably be a good one to look at.
But like i say, start slow. Get the right notes playing , when they're meant to be, then slowly build it up to tempo