Ugh, I can relate! I practiced, practiced and practiced some more. I took a class. I read other people's suggestions. The idea of manipulating the quilt in a smooth, flowing manner just didn't seem realistic for me. I started paying someone else to do my stippling. Now I have a long arm, and I can stipple pretty well! I think my brain gets the idea of moving the machine (pencil) but not the quilt (paper).
I hope you eventually get it, but if not, you aren't the only one. Good luck!