Dear Francesco,
If you regularly play the same course, I would suggest this exercise to get dominance over the greens:
Identify the longest dimension of each green, and putt two balls from one fringe to the far fringe, walk across the green, and putt two balls back across the green to the far fringe.
This exercise is to help you dominate the green, so you can relax with your ability to control distance on any "shorter" length within the confines of the green. This goes hand in hand with learning the green speed, which I have suggested can be done with the "Core Putt" exercise. When you know the maximum stroke that covers the green from fringe to fringe, you have an easier time managing any shorter putt.
Also, remember that distance control or touch is informed all during the time you are on the green (walking onto the green to mark your ball, waiting for others to putt, scouting the putt from different perspectives, entering your routine proper to sight the line from behind the ball, etc.). The "stone cold" technique is only the last piece of the puzzle, sort of a coup de grace for touch.
Also, it helps if you treat the greens on the course no different than the practice green, except a little different in shape and contour. This attitude helps you have less worry about your touch, and this lets your natural instincts work like they're supposed to.
Thanks for letting me know, and keep me posted on your progress so we can get it right!
Cheers!
Geoff Mangum
The PuttingZone
http://puttingzone.com
Golf's most advanced and comprehensive putting instruction.