The overclockers at Hardware.info published a nice guide on how to sand or lap your CPU for better cooling performance. The TL;DR is a temperature improvement of 5.3°C on air after sanding both the CPU and the CPU cooler. In the guide you will find all the explanations you need to get started on sanding your hardware.

Good luck!

Full article: http://uk.hardware.info/reviews/5995/workshop-sanding-cpu-for-better-cooling-performance