If this is a home and there is not an upstairs room - you are in luck. You probably do not need to do much more. A double layer of sheetrock is still best. Perhaps, instead of a double layer, you can just floor the attic space above the room and achieve good sound proofing. Noise reduction should be sufficient, since you have an air space and then a roof which provides additional sound proofing.
If you have an upstairs room that you need to isolate from the lower floor, there are additional concerns. This is a case of probably using resilient channels, Green Glue, or other assorted sound proofing materials. This is especially true if you do not want to hear the upstairs footsteps, etc. There are several companies that can help you with this type of sound proofing - at least one or two are on the links page.
Continue to Other Soundproofing Materials.