Soundproofing a common wall

Has anyone soundproofed a wall in their apt? Was it effective? My bedroom wall is a common wall with anoother apt and I can hear my neighbors TV and footsteps (its a duplex and I think their stairs are up against that wall. I've heard from some people that it helps reduce noise and others have said it doesn't If anyone has done either,can you please let me know how successful it was (and how much it cost). Also, what method you used. I know there is that foam you can use, but I dont think thats an option for me. I would have to go with some sort of padding or other type of insulation. Thanks!!