Well hey there buddy, glad to see someone trying to learn the knuckleball. I prefer not to be called a knuckleballer because well that’s the wrong way to think of it, think of it as a pitcher who throws knuckleballs.
It doesn’t matter how you throw it as far as your grip as long as you are getting results, play with some other ones but find your consistent one. Nobody throws it exactly the same but some of the important things are that you need to keep a stiff wrist, you need to follow the ball, don’t push it but follow it out of your hand. Don’t lob it make sure you still throw it somewhat hard, no velocity means no movement. Anywhere from 50-75 MPH will get you some movement. Even though the knuckleball is one pitch you need to mix speeds with it, throw some hard and some soft, just because you have a knuckler doesn’t mean you are good, you have to know how to pitch and just use the knuckleball with it.
As far as the flat ground question, that’s how I started out and it is a good way to start, just get the feel for it. Remember to experiment that is the main thing you need to do. Find what works for YOU.
If you want more help go to www.knuckleballhq.com there are some good knuckleball helpers on there. I would also suggest buying the knucklebook. Now get your butt out there and don’t let it spin.