Double denim generally is seen a bad fashion no no, if you are going to do it, make sure there is a big difference is colour, dark blue jeans with light denim shirt and break it up with a white t-shirt or something or you'll look a bit like the Cookie Monster.
Yeah I know but the jeans as I am would wear it with are black jeans but slightly faded so it would not look like double denim at all.
*edit* I am a bit drunk.