As a general rule, grounding will not affect operation of dimmer.
Type of dimmer, type of switch being replaced, type of load, and how you connect wires will affect dimmer.
Here is Lutron dimmer switch page
http://www.lutron.com/Products/StandAloneControls/Dimmers-Switches/Pages/DimmersSwitches.aspxWhat is the load? Are you wiring dimmer to a ballast? Or fan? Or incandescent lights? Or florescent lights?
Are you replacing a 2-way or 3-way switch?
What color are your dimmer wires?
How many wires were connected to switch?
Can you re-install the switch, and know where each wire went?
Did you replace a light with a fan, and then want the dimmer to slow the fan? Not every dimmer will work with a fan, or florescent lights.
Dimmers cannot dim LED lights.
If I know what type switch you are replacing, and the type of load you want to control, and the specific dimmer you have, I can answer the question.