This page exists to collect resources on Calibration. This includes print refinement and general improvements in quality of 3dprints.
General Calibration
https://printedsolid.com/blogs/news/tagged/a-solid-foundation
http://www.matterhackers.com/articles/retraction-just-say-no-to-oozing
http://3dprinterwiki.info/wiki/wanhao-duplicator-i3/duplicator-i3-calibration/extruder-steps/
Frustrating calibration issues on SeeMeCNC Forums
Optimal Layer Heights on 3DPrintWiki Most of this information is applicable to a large variety of printers since 8mm lead screws are in common use.
PID Auto Tune
PID Autotune Temp Too High (Rostock MAX v2) (SOLVED) on SeeMeCNC Forums
PID Autotune failed!- Temperature too high on SeeMeCNC Forums