David,
I typically go 120-220-320-400-600 grit. I sand each grit at 800 rpm and then turn off the lathe and sand with the grain before going to the next grit. The 120 is for sanding out all of the ridges and rough spots that remain after turning the call. The following grades are just for taking out the sanding marks left by the previous grade. If you don't get a ridge out with the 120, it will still be there when you finish with the 600.
I am teaching my 11 year old great nephew to make calls and I always tell him "feel with your eyes and see with your fingers". Some flaws you see but you can't feel, others you can feel but you can't see. They will all show up when you start finishing.
Take your time, you'll get there.
Brent