Some general tips:
-It is VERY hard to make any isolation differences in an exisiting room without a decent budget and space. Basically, the room needs to be airtight to isolate the sound (this does not account for structure-bourne vibrations that will leak through to other parts of your domicile).
-More mass will isolate the sound even more (ofcourse, if the room isn't airtight, adding more mass doesn't do much - sound travels through air, mostly).
-If you're trying to keep from disturbing the room above you, the best you could probably do is to add padding underneath of the carpet upstairs. Barrier mat is probably the best way to go (though this thick rubber material has to be special ordered, and is probably on the expensive end).
-Also, you're mostly going to suffer from lower frequencies leaking through (vibrating through the building). The best way to deal with this is to add thick, dense material (look into 703 Owens-Corning foam, or for even lower frequencies, 705 foam) onto the ceiling. You should also add more mass and stablize whatever you add with the foam to decrease the amount of vibrations. A cheap and acceptable method of treating bass is the panel trap. You can read about this absorption method at
www.ethanwiner.com/acoustics.html, among many other interesting topics that you can learn from.
These are only some generally accepted tips, but should help you to understand the elements of soundproofing a little more.
