Some pitchers move one or both fingers slightly inward from the seams to get more sinking action.
This pitch usually drops sharply but is slow and difficult to control. If you have good arm action, the basic two-seam grip should give you all the sink you need. Just a few of inches of sink on a two-seamer will yield many ground balls. Experiment with variations on the basic two-seam fastball grip and see what works for you. There are also several versions of the cut fastball.