Putting Fundamentals, the importance of grip and setup
Every year at the beginning of the school year or especially summer camp, cleaning up fundamentals are a big part of our job. The main area of poor fundamentals in putting always starts with the grip. If the grip is not corrected then the trickledown effect of errors grows for the player. Poor alignment of the forearms, then shoulders, and eyeline are other areas, we see daily.
The grip is a great place to start in making changes to fundamentals in putting. The grip should be unlike your fullswing grip by not being in the fingers but rather in the lifelines. By more in the lifeline, I mean in the palms and pointing up the forearms, this can be an awkward position till you get used to it. The putter should appear to be an extension of the forearms. This position is the key to using the face of the putter effectively and not over rotating it throughout the stroke. From here you can choose how to attach your fingers as you wish, the most common grip in golf is the reverse overlap (lead finger over the trail fingers). Most other variations offer no mechanical advantage but are more of a preference based upon the players habits.
Once we have a proper grip of the putter the next part should be easier and that is aligning the forearms and shoulders. Alignment of these two areas helps with consistency of your path (there are other factors involved here as well). Eyeline also influences the path of the putter as the hands will tend to follow the eye direction. Eyes aligned to the left (right handed golfer) go out to in with the path and right go in to out. In any of these instances the player will make a compensation to make a consistent stroke.
When starting with these basic fundamentals, your putting consistency should also improve.