It tends to be more expensive to shred paper prior to recycling, so it is really important that only classified materials are segregated for shredding.  It's vital to have a simple system in place to capture non-confidential paper for recycling alongside a system for storing waste classified paperwork; if you don't, you could be spending alot more than you need to be to deal with your paper wastes.

Try to ensure your confidential paper is stored in bins or cabinets with slim, letterbox slots for posting materials inside; this will help to reduce 'bulk' dumping of huge wads of non confidential materials. 

Only shredding what needs to be shredded will use the correct amount of energy that is actually required for the job; shredding lots of uneccesary materials will waste electricity and have a negative impact on the environment.