On my Genie's coarsest grit diamond wheel (80 grit), I start grinding the edges into the shape I want. Occasionally, a stone is too "soft" and if I know it will flake or grind too quickly, I'll start with finer grit to slow down the shaping process. Here I'm taking the edges down to a triangular shape on the diamond 80. (Side note: my Genie has six grinding and polishing wheels: 80, 220, 280, 600, 1200 and 3000 plus two buffing pads that I rarely use.)
I know that there are a bazillion other lapidary people out there who are more detailed and scientific in their approach to rock polishing, shaping and beyond, but this is the process that works best for my stones and me. I can really get into a groove sometimes and lose myself in the grinding and polishing but the best part is ending up with some spectacular stones and having the satisfaction of creating a piece of jewelry from beginning to end.