There are some great pointers made already, i'll add a few more.
Sound is directional until you hit lower frequencies and with engines, gearbox's, drivetrains, road noise and all sorts of other things, one type of sound deadening will struggle to eliminate all noise.
You need to incorporate various types and understand it's usage.
Stiffening panels is a good start. Using products like silent coat or dynamatt will help in this way but use it sparingly. Pictures of footwells or the underside of the bonnet plastered in the stuff is purely a gimmick for you to part with your cash. Any company doing this deserves avoidance. You want to stiffen the panel, so add 2-3 inch strips until the panel has a more ' dead ' sound rather than a tinny sound. Remember these products don't stop sound travelling through, they provide stiffness and thus help reduce flex and vibration which comes across as ' noise '. ( point to note, the product can provide a barrier to noise as they have mass, but it's tiny and would prove very expensive to use it to eliminate noise alone )
Foams like a closed cell foam help absorb it's effects but they work best when left exposed. If you cover up a foam then you reduce it's ability to soak up noise and here is where it becomes a little difficult to balance everything with foam and stiffening alone.
The final part is Mass. Providing a mass that will help absorb sound is another way to quieten things down. Using dense rubber stuck to the panels underneath a layer of foam will help quite alot. I've used rubber mat's to drop the lower frequency ( bass from a speaker ) from travelling through walls etc.
I would use a stiffener to the panel first, then a dense rubber mat and finally a closed cell foam on top. This work's in the cab area very well but it also highlights other problems like the seals around your doors as suddenely they are much more noticable.
For the bonnet, i really wouldn't waste any money on it personally. The noise outside the vehicle is not going to change the noise you hear inside..the engine is sat in front of you with a thin piece of metal to stop the noise between you and it. I stripped out my dash and found land rover's idea of sound deadening laughable as it wasn't even covering the multitude of gromets and holes in the bulkhead and of the square meterage of bulkhead, about 40% was covered by their effort from the factory (2011 model ).
Landy's were designed to be workhorses, they were never designed to be quiet inside but you can get them to a decent noise level in the cab with some simple practices.
A few links to help;