Here you will find some useful resources to help learn to use and tune your RepRap.
Print Quality Troubleshooting
There is a useful guide to fixes for specific problems on the RepRapWiki:
Simplify3D, who make proprietary slicing and printer control software, have put together this Print Quality Troubleshooting Guide:
An old but good guide to Slic3r settings and extruder calibration from RichRap (Richard Horne)
Guide from Think3DPrint3D to setting up your Marlin firmware - how to edit Configurtion.h
YouTuber Thomas Sanladerer has a fantastic collection of video guides and reviews.
Triffid Hunter's calibration guide
Another very nice rundown of designing for high quaslity 3D print from 3DVerkstan:
If you want to add more here, or you are aware of any inaccuracies or better, more up to date guides, please contact the group here and ask for Alex or another Admin.