We need to first analyze what you actually need.
 
Soundproofing means denying sound access to an area (ie: prevent sound from leaving your location and annoying the neighbors, or preventing outside sound from infiltrating your studio). This is generally done with mass. Heavy lead sheets between multi-layered drywall, or walls filled with sand or concrete. And airlock-style doors.
Sound deadening is preventing the sound within your location from bouncing around and reflecting back to the source (ie: egg crates, foam panels, bass traps etc).
 
Which solution you choose depends on your definition of sound proofing.
 
If you’re looking to tune the room and minimize flutter echoes and reflections within your studio, Auralex has some great pre-made packages that you can setup without needing an acoustic engineering degree. These packages are excellent because they’ve done the work for you. Most beginners cover their walls with all sorts of bits of foam but this causes a problem: it only addresses the high-end of the frequency. Remember: foam will only absorb the higher frequency range while the mid and low-range (bass and sub) will still bounce around like kangaroos during mating season.
If you’re going to add foam, you must also add bass traps. At our studio we saved tons of money by building our own traps. They’re super easy to make and also allow you to really customize the size and colors as needed.
 
You can easily find bass trap build plans online: