Where to start, let me see pics of your room and what your thoughts and ideas are...also what you wished you had done. I need to reduce the amount of volume escaping the room. Thank you gentleman!
Installing seals around doors, and sealing up any gaps will help isolation.
Isolation requires mass and no air-leakage. The most efficient use of mass is through a mass-air-mass system.
If your room is finished, you probably wont want to install a second, decoupled, room within. So you will have to seal up any gaps, sort your weak links, and be happy with it.
Weak links can include, doors, windows, roofs, etc.