Step 1: Buy Material GTMAT Automotive Sound Deadener
GTMATAutomotive Sound Deadener, it's cheaper than dyno-mat works just the same. http://www.gtmat.com
Make sure your measurements are correct, and have the enough material to cover whole vehicle.
Step 2: Cut Matrial Into Smaller Pieces.
By cutting into smaller pieces it allows to fit in corners and edges easier.
Using a box cutter, then placing cardboard underneath to cut smoother.
Step 3: Multiple Layers Near Loudest Areas, Speakers/ Amp/ Woofers
Place multiple layers on top of each other near speakers, amps, woofers, engine, where ever alot of the sound is coming from
Step 4: Cut Bigger Pieces for Large Areas
By cutting bigger pieces for larger areas covering the space is more efficient.