Oiling a paper shredder is a pretty straight forward process & for most home/SOHO paper shredders, it should not need to lubed too often.
Shredder Lab's blog has a great write-up of how to properly oil a paper shredder.
[How to oil a paper shredder]
In short, don't use WD-40 or like lubricants. Most home/SOHO paper shredder manufacturers re-bottle Canola Oil and sell that as their lubricant of choice. Simply hit the grocery store to save some money on your shredder lubricant needs; if you don't already have a bottle in the kitchen.
To Apply: Spread a small amount of Canola Oil onto a piece of paper, using a zig-zag type motion to cover the entire sheet. (* NOTE: don't soak the paper, just apply light even coverage.) Then feed this sheet through the shredder. When completed, reverse the shredder for a few seconds. This will ensure the oil is dispersed throughout the shredder's cutting cylinders. The final step is to shred a few strips of newspaper to remove any excess oil. Repeat once or twice more for optimal application.
Oiling your shredding every now & again (at least a few times a year) will keep your shredder running smoothly, reduce wear & noise, and helps keep the shredder from slowing down over time.