A few key things to note when wearing denim on denim is that you don't want to have too much of a contrast between your shades of blue! (thesilksneaker.com)
There is something very 90's about wearing denim on denim, in a good way. (bykaja.wordpress.com)
I know there are many people though that can easily be intimidated by the thought of wearing denim on denim. (themoptop.com)