I visualize the chakras spinning "normally", like an object would spin, but then I imagine them changing shape as they spin faster. I find this is key in my visualization of the spin.
They might look slightly more circular, start showing trails of their spin, but otherwise look "motionless". You can also imagine the air around them as colorful, and have their spin push away this air visually.
These methods all came to me naturally, through meditation over time. Your intent is what matters, and you will be doing these things better over time. I also had issues with cleaning chakras that "fixed themselves" in this way.