While you might find it best to pull off the denim on denim trend by pairing two different shades of denim, the denim division editorial by men's style Australia lead to me rethinking the idea... although tricky, I however feel that pairing the same shade of denim (whether dark,light or bleached) might work.
- adding detail to one shade. (like leather)
- create a degree of separation (darker belt or tie)
- pairing it up (simple fitted blazer)
well I might be committing fashion suicide, see the editorial and tell me you do not get the same feeling. (see GQ.co.za on modern ways to wear denim on denim)