Step 1: Find The Center Of The Gravity
Its Very good if the CoG (center Of Gravity) is in the same place as the CoP (Center Of Pen)
Step 2: Holding The Pen Right Way
Step 3: The Spin!!!
EXAMPLE : IndexFinger :1 somewhere else on the hand 1
that means your gonna move your Index Finger to that place
hope you get it xD
Step 4: TRAINING!!!
EVER be able to perform this trick without training!
i think ive written all the important!
NOTE : This took me a week to learn (and 2-3 months later i never drop the pen! :D)