Well that can be it but also the downward moving pitches help with that. So the sinker and the change (assuming it has drop) will work nicely for that. Then that cutter thrown inside to jam someone or off the outside corner could fetch a few and the fastball if it has movement could get some.
That sinker and change is what you'll prolly use for most of your groundouts though. Chien-Ming Wang's sinker is nasty, he is one of the greatest ground ball pitchers there is so I suggest you watch some video of him.
I do think that the cutter could actually be your fly ball out or pop-up pitch because just having seen Mariano Rivera pitch so much I've noticed his get a lot of balls hit in the air.
Why just try to be a groundball pitcher though? Just be effective however you can. Don't worry about what kind of outs you're getting just get the outs. If grounders are what come then great but if not, just get the outs pop-ups, fly ball outs and Ks work too.