Everything you need to know for a successful soundproofing job, you may have already learned in grade school. In the classic sixth grade soundproofing contest, each student is given a shoebox and instructed to modify their shoebox so that when an alarm clock is placed inside, the sound level of the ringing clock, measured outside the box, will be the lowest possible. The winner is the one having the least decibel reading.
The exercise is a good one for students and for others contemplating how to professionally soundproof a space. To be successful, you need to consider each path that the alarm clock sound can take to reach the outside of the shoebox, and then come up with a good way to block each and every one.