Extruder Calibration

I'm sure this has been asked and answered a hundred times, but is there a bookmarked post, or resource that explains the various factors involved in calibration? I have the Mendel90 and am still struggling with calibration - sometimes the material comes garbled before it hits the surface, others it sticks and then stretches too thin before it takes any shape...

Searching "extruder calibration" got me hundreds of posts, but most of them seem too specific to pone platform/printer-type. Any pointers will be great!

Tx

[forums.reprap.org]

---

Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse